The easiest is to add them to the entire stay at BCV. You are entitled to add up to 5 adults to a BCV studio and doing so allows access to SAB which I assume is the main drive. DVC not Disney is going to care if they don’t stay overnight.
DVC friends of ours do this often for us. We live in Orlando (ex DVC), but they put us on their ressie. We enjoy many benefits, although don’t actually sleep there, including TOWL access.
It is much more seamless to simply add them to the room in advance, rather than at the FD (especially if the FD designates them as a "day guest" - lesson learned the hard way )
It is much more seamless to simply add them to the room in advance, rather than at the FD (especially if the FD designates them as a "day guest" - lesson learned the hard way )