Play cosmic encounter. That's my serious answer. Sorry if it's lame, but it's better than 5-player Dip. Also interesting in seeing what people come up with though.
Print out an Ancient Med map?

Does it have to be a finished game?

That's an interesting thought, Diplomacy in Axis & Allies style. In essence, it's a five player variant on the classic map, using the same powers. Should be doable.

I'd opt for a variant which is basically a 1903 position with England and Italy in CD, with those CDs split by respectively F/G and A/T. This basically skips the getting-to-know-you phase and jumps to the midgame. One good thing is that A is going to be a lot more balanced, but F might be a bit overpowered. For this reason, I'd make G a pretty hefty size.

Wow, never played Escalation, but it sounds like fun actually.

Not to self: Don't play E/I next to TMOW

Civilization! (The Hartland/Trefoil game); it's rare to find 5 people who have the time and seriousness of mind to play this for the 6-8 hours it needs, but it can be boring waiting for your 'turn'. But for sheer fun and nastiness, hard to beat Junta; if Dip required, then Ancient Med (how I wish I had a hand in designing this!) - one of the best balanced variants.

Play the 2012 World Cut Public Press game from whence it started being 5 players Public Press IRL.

Lol @ Valis :-)
I love to play both, but if you're looking to remove two powers and still have the other powers in decent balance, removing I/E is pretty good.

Actually, removing I/G may be even better. (my two fav countries)

gameID=93086
Start at Spring 1944, less than halfway through when it finally got down to 5 players

<wonders why that sentence isn't ridiculous>
<oh wait it is>

Will that game have a Y2K bug?

I asked the same question in the official thread but someone pointed out some jokers already tested it.
http://webdiplomacy.net/board.php?gameID=15821

I like it, but you can also vary the victory conditions. So if germant is down to two centers his 'win' condition is just to survive beyond the next 4 turns. Meanwhile the france starting on 12 centers doesn't get a 'win' unless he manages to solo... Or similar.

So yes, unbalanced game, but with an attempt to balance the victory conditions.

I actually have a laminated board for Ancient Med.

@Chubles

Yes! The civilization board game is great fun! I find it kind of funny how my two favourite board games are best with seven players but I can usually only find five others willing to spend that much time at a board.

@Valis, i like taking a finished game, and using the conclusion as your 'win' conditions.

So for generating victory conditions
1) take any draw at about the half-way point (or when the needed number of players have been eliminated)
2) victory conditions for players included in the draw are a solo
3) victory conditions for players who were later eliminated in the game are to survive to a draw

How does that sound for a general system? What am i missing out??

not to be rude, but maybe you're missing out that the same game, even starting halfway through, would go vastly vastly different if played in 10 different timelines, much less if different people were playing it?

Making "be part of the draw" as a victory condition is really weak because the original players were obviously going for that and failed, so either they were bad or were in too poor a position to do so.

And requiring a solo to win is again redundant. It's not like the original players if they were any good weren't going for it so they probably couldn't.

It doesn't sound much different, much less better, than just having them play it without altered victory conditions. Or a game where all the powers were roughly even.