I have the RRS B26 plate:
With the plate installed, the EF Adapter cannot be mounted on or removed from the EOS M body - the plate contacts the edde of the body before the adapter can be rotated far enough. However, if you loosen the EF Adapter foot a little bit, there's enough play to mount/unmount the adapter; no need to remove the plate from the foot or remove the foot from the adapter, just loosening the knurled knob on the foot is sufficient to allow clearance.
The EF Adapter foot has a camcorder-style attachment, with a hole for an anti-twist pin:
Arca-Swiss camcorder plates don't seem too common. I've come across the RRS B26 (which I bought long ago for a camcorder) and the Kirk PZ-40; Hejnar makes one as well. Of those three, the RRS is the shortest at 1.6" long, the Hejnar is 1.75" and the Kirk is 2", and the Kirk and Hejnar plates appear to have relatively more overhang at the rear, meaning you'd likely have to remove the foot entirely to unmount the adapter.
Alternatively, you could go with a small standard plate without the anti-twist pin. For example, the RRS BPnS
should fit on the foot with nothing extending behind the rear edge so nothing would contact the EOS M body during monuting/unmounting.
For the EOS M body, I use a small Hejnar plate, pictured in this thread
Hope that helps...