Are you trying to do 1v1v1 or 2v1? I would imagine that you could just set the board up according to the rulebook letting all three players choose where to place objects. Then just divide the board into three segments and place characters that way. Your games may be a bit shorter as you search for supply tokens unless you add in a couple extra. If you mean to do the "campaign" from the days gone by expansion and some scenarios only use one or two figures then just use the alternate point allocation for three figures.