NL parts company BBB has a stem raiser that is internal,
you knock out the Star-nut.
it goes inside the steerer like a quill stem...
But, their bit of cleverness, and TW manufacturing capacities ,
resulted in making a center bolt that pulls up the wedge,
with a 6mm hex allen , but the inside if the hex is threaded..
that thread is the headset preload.. bolt in the cap..
http://www.wiggle.co.uk/bbb-bhp-2021-stem-extender/
Not able to add/attach insert pictures, nothing to see really ,
just a stack of spacers,
on my bike, I stacked 2 stems with the added steerer tube space.
It is a trekking/touring bike any how, not a road bike.. so ..
too heavy a tool for most people.
pannier racks, 26" wheels, lights,R'off, etc..
http://www.cyclofiend.com/working/20...clark1008.html
You could just buy another threadless fork, after all,
this time don't cut the steel steerer down.