Just get some tiny rare earth magnets that can fit in the shoulder joints and a small hand drill. Well, and some super glue (the gel works great). I managed to magnetize a Skitarii Alpha, so SM should be no issue.
Magnetizing is addicting once you get started. My favorite is the 8-in-1 Baneblade.
Drill:
https://www.amazon.com/Pin-Vise-Pre...=1&keywords=model+drill&qid=1596277699&sr=8-4 something like that.
Magnets:
https://www.amazon.com/gp/product/B..._title_dp_1?ie=UTF8&psc=1&smid=A3NKAP522IBO00 I'd imagine SM shoulders a big enough for 3x2mm. If not, you can get them shallower or narrower.
Drill, take a toothpick and put a little dab of glue in the hole (sometimes the fit is snug enough not to need this), place magnet (I usually use the flat end of the drill bit for this), and go to town. Just always be sure to double check your polarities.