I've been thinking about this all morning and I believe I have a solution that doesn't require any new parts. Well, there are a couple of approaches that I can try. I think the best option is to drill and tap the proximal end of the top cap threaded stud. It is M8x1mm on that end (just under the 6mm hex in the top cap) so there is plenty of material for this. You only need a few good threads to hold your decorative (at this point, that's all it is) cap in place so I can probably just drill 5-6mm then bottom tap that hole to make this work.

The other option would be to insert either a trimmed nut or a thread insert into the back of the top cap before the threaded stud is locked in place. There are a few millimeters of open space between the end of the hex and the beginning of that stud (typically occupied by the rubber plug) that can hold the nut/insert. You'd still only get a couple of threads and this requires an extra part plus modifications to either the top cap or the part itself making it less desirable.

With either option, you'd cut the innicycle steerer to be a few millimeters below the top surface of the stem (keeping in mind the thickness of the inni top cap), just like a typical threadless steerer would be cut. It's aluminum so you don't need to worry about crushing it.

M5 thread in the stud:


I'm really liking this actually, and may just add it in as a standard feature to allow people to use custom top caps, something that has been requested previously. The extra cost will be minimal on a production run.

[edit] Re-reading your words, it sounds like this is exactly what you were suggesting.[edit]