I see two options - One is to arrange things evenly so that both breasts rest on top. This will seem more normal, I think.

Second harks mw back to Esther Halpern, then owner of the Gilded Cage, Phily. When she was fairly short and 20 to 30 months pregnant (it seemed) & seated she found the guitar strings hard to reach. She just played side-saddle. I forget if the guitar stayed out front & she turned sideways or the other way around, though. I worked fine.

Many men play banjo at the hip - it wouldn't be that unusual.