Honestly, why is this being asked extensively on the forum? The ground instructor can certainly provide that information to your friend if they just ask there? Why ask a friend to ask on a forum and possibly get bad information? Doesn’t seem like the best decision making out of the gate.
Once they’re in CASS just do it like a normal jumpseat, there is no need to worry about it being must ride. It’s not must ride going back to DEN (a domicile) anyway.