Further suggestions:

All orchestra musicians are members of a Belmont Festival Cooperative
which pays dividends as funds are available.
All Belmont Festival Cooperative Members provide their names,
social security numbers, and addresses.
After the last of each set of concerts, each member tells you in writing 
the number of hours he/she has spent in rehersals and performances.
Powers issues and mails to each Cooperative Member
a check proportionate to the time spent and available funds.
Each January Powers reports these payments to the IRS on 1099M forms.
Powers is remunerated for its efforts: a) by free advertising in the
programs notes and b) by such fraction (2%, 3%, or 5% etc.)of payments made 
as seems appropriate and has been agreed upon.