I think this would be easy if you started with a baby tree although I think the end result would be unhealthy, unsightly, and need to be heavily pruned often to maintain "bush height." Unlike many other trees masquerading through urban yardscapes as shrubs, redbud is not prone to suckering. I think what you would end up with is a constant battle with something that ends up looking and acting like a southern crepe myrtle in the care of an old-school gardener. In case you've never visited the south in the winter, the 2nd pic down at this link will show you what I mean. They do this to the trees at the bank across the street from me and when they grow back, they look like lollipops and don't flower much. Crepe myrtles often don't survive this pruning. A tree that is not naturally succeptible to suckering can not be made into a shrub. It may or may not be able to grow new branches at the decapitation point. One missed pruning and it will get top-heavy and unstable.

Unfortunately, the only practical solution to having a tree in the wrong spot is to remove it and replace it with something more appropriate in size or shape or whatever is bothering you about the 12-ft. redbud.