Ultrasonic cleaners have and are used on enamelling systems insulating aluminum.
I've been a process engineer and a plant manager and we have insulated tons of wire (when you consider the small AWGs there have been millions of feet) with Formvar. We have done everything from less than single build to quad build from 50 AWG to large shapes such as rounds, squares, and rectangulars up to .150 x .660. We have coated shaved rod, dip form, and various types of unshaved rod.
If you are worried about heating the wire too much what are your limits? Like I have said in earlier posting when inline drawing, the preannealer was used primarily to clean the wire. I really think in your case a small tube annealer with some steam would probably adequately clean your wire. If your wire surface is copper, I just do not see why you are having this problem.
richard