Here's a simple PCB holder for soldering or just holding them steady to stare at longingly. I don't judge.
A couple of neodymium magnets holds it in place quite firmly on a metallic surface. This was designed for two magnets 12.7mm12.7mm6.3mm which is what I happened to have in my junk drawer. But of course you can substitute smaller ones or let me know and I can make the hole bigger/smaller.
The little lever (or flipper that I called it for some reason...) is simply used to more easily dislodge the thing after you stick it down. Neodymium magnets are pretty darn strong.
After printing cut a piece of 3mm filament to a suitable length, thread a flipper onto it and jam it into the bottom of the thing. Since filament diameter can vary quite a bit it'll either fit loosely or tightly, or not at all (it's designed for 2.9mm). I'll leave it to you to figure out how to deal with that, glue and or substituting the filament for something else comes to mind.
Glue the magnets in place using epoxy to make sure they really stay in there. Super glue might work but in my experience the "super" part seems misspelled...
If your magnets are too small you can make up for it by putting a fair bit of epoxy in the cavity, then put your magnets on top of some oily plastic (you know the kind that no glue seems to stick to, blister packs usually works), and finally squish the holder down onto it and let it sit overnight. That should fill out the voids and still leave your magnets clean on the underside.
Then, after you're done, you will take pictures of your print to make up for not sending me all of your money (throwing money at the screen does NOT count) :P