I see that you already found a solution but I wanted to add a couple of ideas for future searchers.

I had to cut some signs in this material recently and had neither the correct bits nor time to get them. I traced the profile with a V bit first, then ran the file as normal and had very good results.

There were some through cuts on this same project so I inverted the design and put the face against the freshly resurfaced spoilboard. My visible edges were perfect since the upcut bit was pulling into the plywood from the back side, effectively mimicking a downcut bit. This method doesn't make both sides clean like a compression bit would but it did give the one good side that I needed.