If it's just a couple volunteers, I would build a case and present it to my one-up or c-suite. The ROI would likely be positive. If the hospital isn't willing to waive the fee, is there an opportunity to build a small fund into your department budget for such circumstances?

Barring an option to absorb the cost, is there an alternate entrance they could begin using where parking/access is easier? Could designated "volunteer" parking spaces be carved out to ensure easy access?

We used a valet service pre-pandemic but it was free for anyone using it. Unfortunately, we have not reinstated that service yet due to the cost.