Like ronnie01 mentioned a few posts ago, the RFC guy makes a good adaptor, from nylon of some sort I think. Being naturally thrifty, and handy at times, I made something similar for my 452.
They're not hard to make, the only part that may take some trial and error is the angle of the ramp. You load it into the standard mag like a cartridge, the .22 round sits on the concave top in line with the chamber mouth. When you close the bolt, the top of the adaptor is pushed down by the bolt and slightly compresses the mag follower spring.
While in theory you can simply drop a round on the adapter and close the bolt, I've had better results thumbing the pre-positioned round into the chamber. Less chance of shaving the bullet.
They're not foolproof, unlike a true single shot loading ramp there's not as much concave area to cradle the round. Still a vast improvement over fumbling a single round into the chamber though.