Keeping trunks thin

I’m kicking around the idea of taking my many volunteer mulberries and sculpting them into a garden arch. But mulberries can get pretty large, so I’d need to keep them in check. I’m particularly concerned about keeping the trunks from getting too thick; I’m confident that I can keep them from getting too tall with some simple but brutal pruning.

Are there ways to do this? Most of the information online seems to be bonsaiers looking for the opposite effect.