ABP Templates - Unable set Blendmasks as Inputs/Variables on Child ABP

I’m creating an Animation Blueprint Template to control 2 characters with different skeletal meshes that share the same animation logic.

Problem is:
In the Animation Graph setting up a Layered Blend Per Bone node.
It won’t let me set a Blendmask because no Skeletal Mesh has been set.

I tried copying the node from another blueprint and it looks okay, but it will only work for the skeletal mesh I copied from, not for the other meshes I want to share this ABP with.

Any ideas how to allow blendmasks to be picked on the Child ABP?

Thank you in advance!