Enabling blend modes with faceSubstitution

I’m successfully compiling the faceSubstitution demo on github using ofx 0.9.
Created a working 0.9 fork here>

My next goal is to enable blend modes on the tracked face image but have had no luck so far.

On examining other examples using ofEnableBlendMode I see that they all enable a blend mode at or near the beginning of a draw call, and then disable the blendmode at or near the end of a draw call.
Because of the various masks used in the demo its not so straightforward.

I’ve tried every permutation of enabling and disabling blendmodes using ofEnableBlendMode but so far have had zero luck. I can get blendmodes working on the entire image(webcam stream) but not just the masked face image.

Can any ofx experts possibly have a look at the github source and offer some suggestions?
Should I be focusing on the draw calls in the Clone class? If so, where exactly should I be using ofEnableBlendMode ?