Also don't forget the play rules on page 26 for accelerated gameplay. I think any group who has played the game once can implement the first rule of "simultaneous first turns" without any issue.
Easier Ascension also has decent merit (i.e.: 4 culture = 1 ascension, instead of 5 culture).
Those alone probably will drop the game's time by maybe 20-30 minutes, making a 3 player game finishable in 2.5 hours.
However this comes PURELY from a theoretic standpoint. I just ordered the game yesterday and am annoyed how long I'm going to have to WAIT FOR IT TO ARRIVEEE!! KLINGON RAGE!!! KLLLLIIIIGGGOOONNN RRRAAAAAAGGGEEEE!!!