Permits are non-transferable, for cost or for free. Turning the unused spaces in to the permit office is the way to handle this.
CaT
If future generations are to remember us with gratitude rather than contempt, we must leave them more than the miracle of technology. We must leave them a glimpse of the world as it was in the beginning, not just after we got through with it.
- Lyndon Johnson, on signing the Wilderness Act into law (1964)