Have you tried the Raco 976 metal goof rings? I used them a few times in the past and they seemed to have a slightly smaller profile than the plastic extension rings. They work with one or two-gang switch boxes, one-gang handy boxes and one-gang plaster rings where the device is centered, so maybe they will work with two-gang plaster rings.
I know those plastic Arlington BE1 and BE2 rings generally work okay with two-gang plaster rings for depths greater than around 5/8" or so, but because they are tapered like a wedge, I find they usually don’t fit well and the screw holes don’t align properly with the plaster rings for shallower depths less than 5/8" without some cutting and modifications.
If you’re using the two-gang BE-2, you might have better luck using two of the one-gang BE-1 extensions, as that might give you a little more wiggle room for adjustment.
Raco 976 
