I would just move them to cooler storage area and not remove sprouts until planting time. I have planted dahlias with long sprouts and they do not seem to sprout out of the ground very much earlier than the short sprouts. I believe it is the formation of the feeder roots on the other end of the tubers that gets them going and that only happens in the warm, moist soil.

I leave my dahlia tubers in the ground and mulch heavy for the winter and have had good luck with this method. However this year one has put up a shoot through the leaf mulch. This was a new tuber last year but I've never seen a dahlia break dormancy this early. It has been a mild winter but not that mild. Has anyone ever seen this--I've been growing dahlias for 30+ years and this is a first. I think I'll just wait and see what it does.

I would pot those babies up in gallon pots and let them start making roots. And I would probably keep them in the greenhouse. Just don't overwater. I pot mine up about now and keep them fairly warm, but barely moist. Make sure they do not freeze or drown. If they grow too tall before planting time just pinch them back. I do this with all new dahlias and get blooms about a month earlier then usual.