It looks like there is going to be one more high profile cameo in The Hangover 2 and that is going to be from Paul Giamatti. He is scheduled to fly to Thailand in a few weeks to join Todd Phillips and the rest of the cast to film his part.
Giamatti is currently generating a lot of buzz for his role in Barney's Version. Right now he is playing Ben Bernanke in Too Big To Fall for HBO. Giamatti be seen next in the Tom McCarthy-directed Win Win for Fox Searchlight.