I don't have such a tree, but I don't think heating cables are a good idea. It would be hard to control the heat--too much heat is as bad as too much cold. If you are pushing the envelope on growing zones the best thing to do is give it winter protection by insulating it, something like northern gardeners do with roses, except I wouldn't use soil.

If it has survived 2 winters it must be in a protected location and shouldn't need much protection for the winter. A box filled with leaves or mulch around the bottom would protect the roots and burlap around the top will protect from wind and drying out. Don't mulch until the ground is frozen and little critters have found a winter home. You don't want them taking up residence and munching on your tree. What you would do when it gets too big for these measures is anybody's guess.

Don't count on getting cherries just because you give it winter protection. A tree only bears fruit when it is big enough to do so. In your case as you said several years.