Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:1988547.
I'm not super happy with this, but a couple of people have asked me to share it already so here it is. This is based on Allted's drag knife mount for his amazing MPCNC, but modified to work with HicWics quick change mount.
It pretty much needs to be printed with support. I've tried a few variants that print without support in two pieces (which I included) , but I couldn't be bothered to design a way to bolt them together and I don't trust glue so didn't pursue those. Printed in ABS with support this works, it's not perfect but it works. I'm using this ultra cheap (<$9 delivered) drag knife: http://www.banggood.com/Vinyl-Cutter-Plotter-Holder-with-15pcs-30-45-60-Degree-Blades-p-1098046.html?p=7J301012375920130163 And honestly I can't really recommend it. It's not horrible, especially for the price, but it's not great either. The "nose" was a little rough and had some bits of aluminum hanging off so I had to clean it up a bit to get it working.
Hopefully I'll work up a better mount at some point, but probably won't bother until this one breaks since it works for me for now.
I whipped this up in openscad with measurements based off of allted's original design with modifications to fit the knife holder I got off banggood. Openscad files included and improvements are strongly encouraged. The _v2 version is the one I'm actually using.