Took about three redesigns, but I’ve found something that works with minimal modification to the Reform case.
Uses a pair of M2x6 screws, replacing the M2x4 ones toward the back on the port panels, and two 8x4mm magnets. I also had to file notches in the power plug and HDMI openings in order to route the wires into the chassis.
Not really sure how to copyleft license these sorts of things, so I’ve just adopted the same license used by the Reform.
STLs and OpenSCAD source are here: http://lyk.so/reform_antennas_mod.tar.gz
Tarball SHA256: 8c6d34f7d5bf0d2c2df262466452ca6c942cb098b4aaed18f1b468aebaf25b3d
There are probably still some rough edges to the design that could be smoothed out, but I’ve satisfied my own needs with this for now. Let me know how the design works for you if you use it, and whether you make any modifications!
Edit: My mind seems to not quite be done with this problem, and I’ve thought of a new design that might be a bit better in some ways. I’ll report back once I’ve had a chance to pursue the idea.
Edit 2: The new design’s definitely worse. I’ve learned that the separation of the mechanism for extending the base and rotating the antenna is important, as the two have different friction requirements. I think what I’ve arrived at is about as good a design as I can come up with given the space and material constraints.
Edit 3: I referenced this in a post above, but for clarity: I’m using these antennas here.