I'm not encouraging bad behavior, just saying it would work and it's a leap better than tin foil.
Coming from the world of RC's and Custom flashlights, I've done or seen it all. When Li-ion batts were first introduced we used to charge them in a 5 gallon bucket of sand, even with an intelligent charger. I've seen my share of mushroom clouds before they properly manufactured venting holes in them. Even now, with balanced chargers and multiple protection circuits, most RC'ers still
buy charging bags to charge LiPo's in, so when a battery vents it won't cause a fire. (As a side note, IMO, mech
mods with venting holes in them are a bad idea. If a batt vents, you don't want that kind of vape or heat to get out so easily. We make flashlights to contain battery vents not to let them out.)
Flat top batts are dangerous because most of them don't have that magic circuit under the button that prevents over current, over charging, shorts, and over discharging. Without the protection circuit they are no more than tiny time bombs.
Just to be clear.
I was kidding about the solder Buy good batteries and don't take the unnecessary risk.
Best regards,
Randy