Here's a second coat of wood filler on the test parts.

Initial cleanup.

...and a third coat. This is actually looking pretty good.

I hoped the fillet would stay stuck to the bottom plate and separate cleanly from the side plate. It worked just as desired.

...so I went ahead and applied wood filler to the mold. Application and cleanup is quite a delicate process because the wood filler is thinned with acetone, but acetone also softens the contact paper and dissolves the contact paper adhesive. This is quite a time consuming process.