I have 2 Linksys WRT54GL routers flashed with DD-WRT. On each I have a different ISP, and thus a different private network. I would like to be able to talk to either network regardless of what network I am on.

Example:

ISP1 -> Router1 -> Client

ISP2 -> Router2 -> Client

What I would like to do is something like:

ISP1 -> Router1 -> Client
             ^
             |
             v
ISP2 -> Router2 -> Client

This would be ideally because then I don't need to introduce another device in the mix, unless I have to.

But I guess the first question is - is this even possible?