When I played badminton I used a tennis elbow brace. It grips the tendons and prevents one getting all the stretch. They recommend max 15 mins before releasing the pressure and letting the blood flow, not that I listened. It helped short term. Long term was probably avoiding rest, playing through it (as per advice from an England/International coach.
Not sure how it translates to banjo bashing though. Maybe it also depends on which tendons and if they are stretched or detached or it is the sheath they slide in.
What is yer day job/hobby? If it is a gripping sorta thing (spanners lump hammers etc) you gotta watch that, I know it was the source of my woes.