Richard Franiec has expanded his line of grips to include one for the EOS M camera. These are high-quality anodized aluminum grips designed specifically for the camera in question. Price is US$34.95 for the grip.
I've used Franiec grips on several cameras and find them of high quality and just right in terms of providing additional grip. They are available for the following mirrorless cameras (all of which need some form of additional grip, in my opinion): Canon EOS M, Nikon J1 and V1, Olympus E-PL3 and E-PM1, and Samsung NX200.