I recently had a similar problem (needed 3 DuBro extensions to clear the fuselage ).

How I solved the problem was:

1. Get a length of 3mm threaded rod. They usually come in 3' or 1 meter lengths for under $10. I had to mailorder mine since none of the local hardware stores had any.

2. Get 4 3 mm nuts.

3. Double nut at one end of the rod. Make sure you use HIGH TEMP threadlocker OR solder the nuts together. Use your dremel and cut a slot about 2/3 of the way through THE TOP NUT ONLY for a screwdriver.

4. Cut the rod to the length you need.

Hope this helps.