Is it possible to keep a request in the Build Queue until a certain (script defined) criteria is met ?

I have a configuration that I want to run concurrently but block concurrent runs for build requests with identical variables. I don't want to throw out the request (as I could easily do in a Pre-Queue Script) but instead want to allow the request to be queued up but not run until the duplicate request is finished.

Thanks for any help you can provide,

John