While you can find 1" threadless (non quill) configurations of a fork steerer, I can't recall ever seeing or hearing of running threadless stem on a threaded fork... indeed, the very nature of the materials used and their configuration (threads on a steel alloy steerer vs a star fangled or similar device inside an aluminium or carbon steerer) makes it dangerous to impossible to do so (a threaded fork would be cut to handle just the stack height of the headset used whereas a threadless fork would be cut to handle both the headset stack and the stem stack plus any additional spacers if needed). Using a threadless stem over a threaded fork steerer could cause metal fatigue (at least) and eventual catastrophic failure or (at least) the inability to adequately secure said stem!
Are U sure it's not a quill stem as well?
Anywho, go to Chris King's website to check out their alternatives. They do offer a bit of flanagalling, though not what you've described.
In some instances, I've been able to convert, via their "kits" a 1" threaded to a 1" threadless or a 1 1/8" to 1"... but this is just the headset and assumes that I've got the compatible fork and stem.
At one point, CK had a Perdito system that was supposed to address some of the shortcomings of most internal designs (mainly, the possibility of trashing an entire frame due to an ill installed or ill maintained headset) but since it was proprietary too, it would require a framebuilder to design his/her frame for just that type. I'm unsure if they still make it (say, for smaller builders and DIYrs) or if any major builder ever used them. CK may not have gone with one or more of the internal configurations because of licensing issues and the possibility of putting a nail in their own coffin.
BTW, the phrase hidden headset kinda describes the trademark name for Campy's Hiddenset which is also proprietary and not compatible with say, Cane Creek's IS system... all requiring a headtube manufactured to particular configurations... not interchangable.
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