Discussed with Stefano...solution is to use Bullseye routing. Assign both Skills A and B to agents in Ring 1, then roll to Ring 2 after specified number of seconds and strip Skill A from the call. Agents in Ring 2 just have Skill B.
In Architect, Transfer to ACD and assign both Skills A & B to the call.
Stefano, please post back here after you verify it all works. Thanks!