My band frequently requests that callers do this when we play, at least once or twice in a night.  We'll be doing that this coming Friday at Glen Echo, with Greg Frock calling.  Gives us a chance to play our hornpipe / 48-bar-jig / slip jig, or whatever, sets.  If you'd like, I'd be happy to put you in touch with some of the callers who have accommodated that practice.  Some contra dancers complain if it's more than a dance or two in a night, but most of them enjoy it, particularly if you don't tell them it's not a contra dance.  They're certainly not any more liable to complain about a ceilidh mixer than about any other mixer.