Chuck Lukas was looking for a method to deodorize an upright player
piano.  One method that worked well for me was charcoal.  I am
uncertain if briquettes work better than chunks, but all you have
to do is place some chunks in an open bag around suspected spots
where the little rodent(s) would congregate and then close up the
piano.

It doesn't work quickly like Fabreeze or other air fresheners, but over
time (maybe six months) the odor does reduce and eventually disappears.
In six month's time, the weather should be more amenable to working on
a piano anyway!

Best wishes from the now cold north near Buffalo, New York

Mike Walter