If you are required to maintain your professional credentials in order to volunteer services to a "qualified charitable organization" (fyi, not all 'non-profits' are 'qualified charities'), you could claim the costs as charitable contributions ("cash") and allocate them accordingly to each of the non-profits. You would, of course need to itemize deductions but this avoids the 2% limit.
(If you are not required to maintain your professional credentials, then I'd suggest the non-profits make that a requirement - in writing).