A few options I can think of:
1. Cycra DX only have an inboard attachment point, and may be easy to install while leaving the bar end weights intact. Can't guarantee they're an easy fit on your bike though.
2. Barkbuster BBZ seem like sort of a mix between handguard and bar muff. It comes with its own metal support if you don't have handguards.
3. Make a small support with a wire coat hanger, or a bracket you might find at a hardware store. Attach it between bar and bar end weight.
4. Bolt the muffs you have between bar and bar end weight.
I don't like option #4 for here, because I may want bar muffs in the cold morning, but not in the warmer afternoon. That's a big reason I don't use muffs at all, though the BBZ might be less annoying than some: I don't think your hands are buried as deeply inside those as in some of the others.