Is it possible to set up an dhcp server to trace the route and depending of the router unit it came from to assign the gateway needed to be used by that part of the network.

I have 2x dsl routers "router a & b" at work and from there I used mikrotek routers to obtain Internet at home "router a", but now a friend wants to join but he will have his own dsl line "router b" but i need to set up dhcp for both because some of the people only knows how to switch the computers on.. any suggestions?