Anyone know of a shoe stretcher that stretches the heel/back part width wise?

the back part of my boot needs to be stretched width wise, because I get blisters all over the back of my feet.
Anyone know what I can do to stretch them? I saw those "tree stretches" on ebay as they're called but they are too long, I don't want the calf part of my boot to be stretched just the bottom back heel part only, any other shoe width stretching things I can get for that area only? or that I could DIY ...just anything, I desperately need the width of the back heel of my boots to be stretched, I get blisters I can't even walk in them for too long.
I tried stuffing the boot, nothing.

-TY!

A shoe repair store should be able to stretch them @JDI007