Whenever I'm asked about what features to look for in a camera, I tend to state three things: M mode, RAW capability, and a flash hotshoe. The flash hotshoe is because I've tried to do what you want to do without one. It's possible, but it's also a serious PITA, and not the best way forward. I'd highly recommend that you consider returning the M10, and [if you want to keep your lenses and use an EOS M camera] swapping it out for an M3 or M5; or a used M(1), M2--as they all have flash hotshoes. You picked the single model in the EOS M lineup that doesn't have one.
Nearly all flash equipment uses either a sync connector or a hotshoe connection to pass the correct timing signal from the camera to the flash for when to fire for the exposure, and it's tough to get around this restriction.
The only way I know of to do it is to use an optical slave with a sync output hooked up to some device (radio trigger, or a sync cable) that can pop the flash. You then put this optical slave in front of the built-in pop-up flash on the camera, make sure that pop-up flash does NOT emit a pre-flash (because most optical slaves will fire on a preflash; basically your camera needs some way to put the pop-up flash in M mode). And you can fire an off-camera flash, like a speedlite on a radio receiver or with a sync port.
This is very Rube Goldberg-like, inefficient, fiddling, and a PITA, which is why I no longer do Strobist work with my Canon Powershot S90 (I used this setup, along with flashes on RF-602 receivers, but the Yongnuo RF-602-TX triggers I used no longer come with a PC sync port input--you need a transmitter unit that takes a sync input).
