I think that's the key: call the hotel not Marriott. If you speak to someone at a hotel and they permit your arrangement then it's almost certainly going to be fine even if it's esoteric / weird / unheard of / violates the Marriott rules. The problem many people encounter is that Marriott do not provide a clear method for contacting individual hotels so most guests assume (quite reasonably) that booking with Marriott + clear contact information for Marriott customer service means Marriott customer service can sort out any specific hotel arrangements. At best, Marriott support can reliably modify a booking and/or an account but they cannot make commitments on behalf of a hotel, whereas a hotel employee can make commitments on behalf of the hotel. There's always the small chance that a hotel employee makes a mistake but even then, hotels are much better placed to rectify their own mistake.