Not sure how best to seed if you can't rely on /dev/random. I've seen a colleague on Mac trying to generate an ssh (or maybe PGP) key and being required to "type randomly for long enough" to generate random bits for security; not sure what application that was though.

So maybe the thing you need to look at is the device driver code for /dev/random. Everything2 has some interesting information about what it does, and for Linux the source should be in drivers/char/random.c.

Hugo