Given the function of a compression plug, is substituting where a Star nut
would really mess up a carbon steerer-carbon fork..

got the steerer tube length dialed in?

you can use a plug of aluminum (Zn free, no 7000 series)
Machined.. and the center threaded for the 6x1 bolt .
and OD sized to just slip into your steerer tube ..
and epoxy it in place.. 5mm below the top end.