No one would stripe a bike lane on this road because there is an adjacent path, so you have to look for other solutions. One way to control speed on the lane is to make it a truly narrow outside lane--say 8', including curb.

If there is no road cycling group, maybe it's time to start one. It sounds like you might be able to get half of the with half of the trails foundation as members (the ones who support the right to use the road). A little competition among cycling organizations could be a good thing.