According to the terms of the program:

6.3. Rental credits are non-transferable. Free Days are transferable only to other Members and to immediate family members of Member (e.g., spouse or domestic partner, child over the age of 21, parent) irrespective of their membership in the Program. Members may transfer up to three (3) Free Days per calendar year. Once transferred, Free Days cannot be returned to Member's account. Transferred Free Days are valid for one (1) year from the original month of transfer.

Is this something we have to call in to do? Thanks.