Well to be honest Im not to sure either. I think you can request for times when your just so fast you can't slow down (gear?) or need more time to brief the approach. I really don't know just have heard it before from a freight dog.
You can ask tower for it, but they'll have to relay the request to approach. Might as well ask approach.
Never done it, never heard of it. Is there some sort of reference for this in the AIM or IFH?