I'd appreciate any advice, don't even know if this is possible:

Building One has 3 ADSL lines, with 3 wireless routers. Users in Building One switch between the 3 wireless connections as required.

Building Two is 30 metres away, but the wireless signals from the 3 routers in Building One are too weak (thick walls, trees etc in the way) to be usable.

Is there a way to run *one* cable from Building One to Building Two, and allow users in Building Two to also switch between the 3 connections? Without having to switch the cable between the routers in Building One every time they need to do so?