OK - I too, thought you were referring to the post. I have not had a broken wire form, but if it is broken, I think you would have to drive it out. I have had good luck removing the wire form by using a small block of wood as a fulcrum, and put a screwdriver near each bend, pushing down on the screwdriver a small bit at a time. I will warn you, that when the form comes out, it kind of "pops", and will likely carry a bit of paint with it.
Once out, you can see whether the wire form is broken. If not broken, then fill the hole with a flat toothpick and glue, then drive it back in. Use a wood softener to drive the form back in, which should be nearly as wide as the wire form itself. (about 2") Softly tap the wire form down so it goes back in evenly. You should be able to feel when it bottoms out.
Since the wire form moves, I suspect one end is broken, and the other end is wallowed out, so you will need to fill both holes. Getting the broken piece out will not be for the faint of heart - all I can think of doing is using a finishing nail to drive it out of the bottom, fill the hole with a toothpick, and install a new wire form. Hopefully, others can come up with a better method. Good Luck and let us know what you do.