Anyone? ;D
I wanted to go ahead and try, but..in case someone's already done it, I opened this topic.
You need a pseudo-random number generator. In embedded systems a PRNG is usually made with a Linear Feedback Shift Register (LFSR). You can probably find pre-canned LFSR code on the 'net and the operations are straightforward, so porting it to PPC ASM is left as an exercise for the reader.