I was in a band where the bass player was dying to step up and play lead so I swapped with him. It was a LOT of fun.
I have to agree with the people saying to do it simple. I have always loved the playing style of Roger Waters. Very simple and exact. I love when he does the root/octave hits (like Careful With That Axe, Eugene, as a perfect example), how he will play a counter melody sometimes, holding the root/octave even during subtle chord changes. Even his more flourishy stuff (see the descending line he does in the 4/4 section of Money) is still pretty simple.
Alot of my bass playing when I am recording a song, I have found, is actually a variation of something I have heard Roger Waters do.
Have fun with it!