I have never organized an event, but I do recall reading somewhere that at least one event rode in had a special ride for the volunteers.

You could basically have two sets of volunteers, one set would ride in your main event for free in exchange for doing support for the ride to reward the volunteers that made the main ride a success.

The secondary ride could be before or after, and would definitely be smaller scale, but if your volunteers are cyclists, it seems like a worthy benefit... although it adds to the organizational load.