Originally Posted by
nfmisso
If the threads will not fit over the steerer tube; just thread the threadless steerer tube to get a tight fit for the upper cone, then but standard threadless stuff above it. The threads on the aluminum steerer tube will not be strong enough to clamp everything together, but will be more than sufficient to hold things correctly until you clamp everything up. This is approach is a lot simpler and cheaper than the others proposed.
If I understand your plan correctly a lot of the steerer tube would be threaded, including the area where the stem clamps. That doesn't seem like a good idea.