Is it possible to use NAT to make the source of an inbound packet look
like the m0n0wall?

I have three ISPs.  Obviously I can't use them all at the same time
for outbound traffic without some serious trickery.  However I'd like
to be able to receive inbound on all three.  If I source NATed inbound
on two of them I can use all three connections at once.  Anyone have
any thoughts on this or pointers for writing the NAT rules?

Thanks,

Mike