What a number of fiddlers around this area do is a simple (once you get the hang of it!) back-beat chop, usually played close to the frog of the bow. I've found it's easier to lay the fingers lightly on the strings and not form any double-stop chords, just a non-tonal "chuck" which covers all chord progressions and keys.

Alternatively, I've seen some fiddlers hold the instrument like a mandolin and pluck a strong back-beat with their fingers, sometimes with a noted tone, sometimes with a muted "chuck".