I lied.
One more thing I have to say.
I'm not sure what their current network topology is -- if they're using some wireless bridges, I'm assuming they're either using a router at both ends, or they're using a wireless bridge/gateway that uplinks into their hubs and switches. The thing that gets complicated (and you may need to subcontract this out to an IT company of some sort) is that you've got to set up their routers to know when to route to the DSL or to keep it in their LAN. Basically, you'll be looking at two LANs with a WAN connecting them.
Just a reminder... but if it's already working using bridges, you basically would just be replacing those -- so maybe not even a problem.