Nice work. I have been struggling with the best way to deal with the mic plug on the m10 myself. I've been thinking of using a rubber band, but I like your design better! How did you make the plug? Did you mold it yourself?
I did mold it myself, it is not too difficult, I used a small piece of fiberglass PCB (printed circuit board), drilling two holes at the right distance, one for the "active" pin (the mic-in), one for the "dummy" one (the line-in). Some patience to file the holes to fit the plugs and to trim the PCB outer edge is then needed.
I have used a straight 3.5mm stereo Neutrik plug for the mic-in and a cheap 3.5mm plug as the dummy one.
The mold cover is from any suitable plastic shape. I used a Gillette shaving blades dispenser.... You can use anything you like, really.
The two plugs have to be installed in the PCB holes and fixed to it with low profile nuts, I used the plastic cover of the cheap 3.5mm plug and sawed two slices out of it, which were used as nuts.
Then I connected the cable to the active plug (and tested it, it is difficult to undo the mold...).
To ensure the plugs geometry is correct, I have actually plugged this assembly in the M10 and then tightened the plastic nuts (not too much, the plastic slices from the cheap connector are not strong - If you have access to proper metal nuts, the result would be stronger, but it is not really necessary, after the mold the assembly is strong enough anyway) before pouring the fused plastic glue.
Please note that the M-10 must be protected to avoid any fused plastic to reach it. I have used a paper sheet with scotch tape to do so.
At this point, using the fusible glue gun, I poured carefully the glue around the connectors and the cable and made a small mound. I then put on top the plastic cover and filled the remaining gaps with the glue gun as much as possible.
Then a bit of patience to wait for the mold to solidify (10 min, half an hour is better, make sure the glue is solid). The connector can now be extracted, the paper protection removed from the M-10 and, voila'... it's done!!!
This is not too difficult, with some patience and DIY skill.
The result is a stable and reassuring connector, which plugs in the M-10 without straining the sockets and ensures a proper connection for hopefully a long time.
Hope this is of help.
Giovanni