Dynamic Queue Members for this insane idea:

So you want agents to log in on another box at a datacenter and have their calls directed to the office server? Fine.

Have an extension setup that allows people to log in using VMAuthenticate, when they authenticate they are then added to each queue they should service using AddQueueMember. Their callback however should be done using Local/. Ie: have them logged in as Local/100@agents in the queue. When a call is sent to them, set their group to 100-AGENTS for example and check the limit. If it's beyond 1, then use Congestion. If it is not, then do a regular Dial to your office server. That way they will only get 1 call at a time.