Someone used a scope mount drilled/tapped to take rear sight. Gives height OK. Can't remember rifle tho'.
A couple of Sportsmatch AB3 arrestor/ mount raiser blocks might do the job if a HW77 rear sight block would fit them. They'd maybe give you the height you need although the early Tommie cheek piece is a tad high so even if they do the job stock wise maybe not ideal.
Always on the look out for Brum / Venom - Webley Longbow / Tommie rifles and parts.