Much thanks to @RenatoKulman for the original design and for supplying the .stp files!!
Check the DIFFS section for all the changes. Added socks for the standard V6 and V6 with Polisi3D extender.
If you're going to use square M3 nuts just insert PAUSE into the gcode at the first layer that bridges over the voids. Resume the print after dropping the nuts into place.
I used Smooth-Sil 960 high temp silicone mix.
The fit on these socks is rather tight, so be careful and take your time getting them out of the mold. Especially removing the sock from the mock heater block part.
I included the step files in case anyone wants to remix further. One change I would make is to remove the 5 deg slope on the bottom of each mold. I added this to help bubbles migrate toward the vent hole, but I don't think it's really necessary and without it the bottom of the sock will be smoother and will probably release from the mold more easily.
Printing Recommendations: Any material (I used cheap PLA). Smallest layer height you're comfortable with (smaller = smoother = easier release from mold). Split model into objects and auto-arrange. Make sure all objects are placed on their flat sides and no supports will be needed.
Assembly : The only not obvious step is getting the top and mock heater block together. I added two different sized nubs to the top with corresponding holes on the mock heater block. These two parts will only mate flush in the correct orientation. You should be able to tell which way they fit with visual inspection. If you have elephant's foot (printing too close to the bed on the 1st layer) you will need to trim that off of the mock heater block part for the parts to fit.
The author remixed this model.
Diffs:
Supports no longer needed
Added voids for square M3 nuts if you don't have heated inserts.
More coverage over the nozzle tip
No more holes in the bottom part
One of the top holes is enlarged to fit a standard 10ml needleless syringe
filleted mold corners
Added molds for standard/stock v6 and for the Polisi3D extender