As it is a lever , fatiguing the steerer tube to breaking is a concern, with leverage of long stem extension ..

It is possible to add an internal sleeve to the steerer tube to double its thickness.

For a different purpose I gort a intenal Quill as a stem riser , made for BBB it tightens inside the stem,

and replaces the star-fangled nut in the process , it could be completely in the steerer tube ,

or you add a few of the included shims, to raise the stem clamping height ..
Its part # BHP-21, in 9/8" type.