There are customers doing this, so you're not alone. The big thing is the NAT'ing on the PIX. Do you want to NAT twice, which is unnecessary, or do you just create static's on one PIX that map to themselves, effectively bypassing NAT.
If you only NAT once, do you do it on the inside or the outside PIX? It shouldn't matter which one, but you need to think about it.
I don't believe we have any docs on this.