i have had some success with these straps..
http://www.slider-straps.com/
they have made all the difference in the world
with the nyckelharpa//
the original strap put pressure on neck and shoulder
nerves causeing numbness and tingling...
now circulation is not compromised.
you might find these will help you hold the
instrument...connecting them will require
some modification..but likely you can find
a way. good luck