I'm wondering if it would be possible to compile a list of the minimum number of off-island people that would need to be "in on it" in order to get the passengers of Flight 814 onto the plane.

This assumes that the people on the Sydney-LAX flight were manipulated to be on there for whatever reason. I just mean mechanically, who would have had to be in on it. Here's how I see it, so far. (The passenger is in CAPS; the people needed to get the passenger on the plane follow.)

ANA LUCIA
Chirstian Shepherd

BARBARA MILLER (http://www.lostpedia.com/wiki/Barbara_Joanna_Miller)/JANELLE GRANGER
Barbara's doctor.

BERNARD/ROSE
One of the people who told them about Isaac's miraculous healing
Bernard's travel agency

BOONE/SHANNON
Shannon's boyfriend, to manipulate Shannon to get Boone to arrive
Boone's travel agency

CHARLIE
Charlie's musical promoter, who organized the runion that led Charlie to see Liam (and probably arranged the flights)

CLAIRE
The psychic Richard Malkin

Marshal EDWARD MARS/KATE
Someone in the US and/or Australian government

EKO
The guy who arranged Eko's forged travel papers

HURLEY
Hurley's travel agency
Lenny and/or Sam Toomey

JACK
Someone to ensure all other flights are booked
Someone in Oceanic Airlines (to find space for Jack and the coffin)

JIN/SUN
Paik -- Sun's father

LIBBY
??

LOCKE
Melbourne Walkabout Tours

MICHAEL/WALT/VINCENT
Brian Porter

SAYID
Someone in the US and/or Australian government

SAWYER
The Australian Minister of Agriculture (who provoked Sawyer into head-butting him)
Someone in the US and/or Australian government
Hibbs

SCOTT JACKSON
The travel agency retained by the contest through which he won an Aussie vacation

TALLY
Acquaintance of Bernard/Rose
Australian/US government agent(s)
Australian Minister of Agriculture
Barbara Miller's doctor
Brian Porter
Christian Shepherd
Eko's forger
Hibbs
Lenny and/or Sam Toomey
Melbourne Walkabout Tours
Mr. Paik
Music promoter
Oceanic airlines employee(s)
Richard Malkin
Shannon's boyfriend (maybe)
Travel agency (like a Travelocity-type website)

Sawyer...the guy that he head butted purposly got in a fight with Sawyer so he would get deported. Also that cop.
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Sayid -the fbi agents

Think less about who got them on the plane, and more about who got them to Australia in the first place. You have to get them to go to Australia to catch the right plane. Once there, you can limit which plane they actually get on...

Sawyer: it was Hibbs (http://gallery.lost-media.com/albums/ep-caps/season1/1x16-outlaws/outlaws162.jpg) who told him the original Sawyer was in Australia

Bernard & Rose: 3 different people told Bernard to take Rose to Isaac. Who were they?

Charlie: Goes to Australia to talk to his brother Liam who went to a rehab center in Sydney. Wonder who runs the rehab?

Hurley: Hurley goes to Australia after Lenny tells him that Sam Toomey lives there.

Michael: Brian Porter gives Michael his ticket.

Excellent points! I'm updating my post

By the way. it's the Australian Minister of Agriculutre that provoked a fight with Sawyer.
(trivia: There is no "Minister of Agriculture" -- it's the secretary of Agriculture who, in 2004, was a fellow by the name of Michael J Taylor)

As for that rehab center.... I wonder if that's why Libby may have been in Australia...

I think that If there was some conspiracy to get certain people on flight 815, that Sayid is a wild card and was not intended to be on that flight.
If you remember, the US/Australian govt gave him a ticket to LA for the day before, but since no one will claim his friend's body, he tells them to get him on a different flight.
Maybe the govt agents knew he would ask for a different flight, and thus made him think that it was coincidence that got him on flight 815, but I dont give the govt. credit for being that smart.

I dont give the govt. credit for being that smart.No, but I'll credit whoever is manipulating the government for being that smart...

At any rate, this thread is assuming that all the passengers on the flight were manipulated onto the flight. I'm not really interested in trying to parse out who may have been manipulated onto the flight and who may not have been. Let's just assume they all were.

As stupid as Kate's toy-airplane plot was, it was not involved in getting her on Flight 815. She robbed the bank in New Mexico.

Good point!
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I also realized that Liam (Charlie's brother) didn't go to Australia to get clean, but because his wife's uncle offered him a job in Sydney. He ended up getting cleaned up while there, but I think that's incidental.
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I also now remember that Locke was brought to Australia by Melbourne Walkabout Tours, which probably also arranged his flight back.
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Of course, the only reason Charlie went to Australia was because some record company was organizing a reunion concert. That may have merely been a ploy to get Charlie to go to Sydney.