How to force the devices connected to the wireless router to open a web site hosted in a local webserver

Ok, so you can connect a single device to that "router", and it gets a single IP address on the remote network. Looks bad, maybe it's just acting as a bridge. Whatever.

You can use your own router, then; buy one (or get a PC with two network cards and your favourite OS) and give it that IP address on the remote network, then use it to let your own network talk to the remote one.

You'll need NAT, because you can't use plain routing here; computers in the remote network would never know how to reach yours. So you need to setup a NAT router (quite easy with both Windows RRAS or Linux IPTABLES) which has your own LAN as its internal/private network and a cross-link to the other router as its external/public one; configure it for NAT, and add a route to your main router stating that you can reach the remote network through this new router.

A little example (can't draw diagrams now):

---------  -----------  ---------------------------  ---------  ------------- 
|10.1.35|--|ROUTER(?)|--|10.1.35.235 | 10.1.36.42 |--|10.1.36|--|Main Router|->
---------  -----------  ---------------------------  ---------  -------------

The thing in the middle is your NAT device; it has two interfaces, and the NAT direction is towards the 10.1.35 network; so it gets 10.1.35.235 on its "public" interface; its "private" one is connected to your LAN. Then add a route to your main router (the default gateway for your network) stating "to reach 10.1.35, go through 10.1.36.42". Done.

If you got WRTG54 routers, using OpenWRT and WiFi Dog might suit your needs. It all depends on your AP software and Radius server for accounting.

There's also CovaAP that may interest you.

I'll hope somebody will fully answer your question as i am planning a similar setup.

Hope this helps.