Wow - right off the bat, I'd say find a new ISP - any ISP that is giving 
you non-real addresses is ripping you off.

If you can, I would set up the base station to give out 192.168.0.x 
addresses to it's wireless clients. That should fix the problem, 
provided your client has less than 253 devices. Having NAT behind NAT 
works fine, as long as the subnets don't overlap (and as long as the 
first NAT, your ISP, has plenty of portmap space available).

This is all, of course, assuming that the base station does routing and 
NAT correctly.