I'm in a similar situation, and am considering a similar solution to the op's.
Originally Posted by
southpawboston
...you can have a frame builder either replace the steerer tube or braze on an addition, and then rethread the whole thing. However, this will cost significantly more.
The steer tube replacement idea is one thing I am seriously considering; having the tube replaced with a threadless one. Has anyone tried this? About what does is cost? Will I have to completely repaint my fork? I'm considering this for my Colnago.