I've been shaping my small buckthorn tree into an inverted cone, and
one of the main branches has grown a couple of feet taller than the
others. Simply topping the taller branch is going to produce a bunch
of spindly top growth.

But what if I took the edge of a pruner and cut or abraded away some
of its bark and vascular tissue? Is there any record of field trials
using this technique to regulate branch growth?