Hi, I'm in need of some professional on this topic..., any help or heads up would be nice. [English not my native so if I say something wrong, please forgive me]

we got this RB750G in out office , I want to use it as a web proxy to gain some control over my network users. when I set up the router for web proxy and redirect traffic to port 8080 , everything worked fine. the problem starts when I try to route users of web proxy to different route table, there are 2 internet modems connected to ether1 and ether2 of the router.
I configured the defualt gateway for ether1 so the router it self connects through this modem (ISP1), I want my web proxy users connect through the 2nd modem (ISP2) .

without the proxy its easy just route them to another Routing table, and use Nat to that particular interface.

please if anyone know how to do this, help me out. I'm stuck and cant get it to work.

you should catch traffic from the router (in output) that goes to port #80 and redirect that traffic to ISP2 or wherever you require