Actually, I bet it would work just fine even if the OP were ordering one 4 day award cert. Since the 2 stays are contiguous nights, Marriott tends to view that as one longer stay even if there are multiple reservations. So I bet the hotel in question would still take one 4 day award cert in that situation.

Don't forget that award nights actually don't have to be contiguous either. I have made reservations where I stayed more than 7 nights with one of the middle nights being a paid night due to no standard award availability. I had no problems using a 7 night award cert plus paying for the middle night in there. In those situations, if I remember correctly, I actually went online and made three reserations. Something like a 3 night award res, then a 1 night paid res, then a 4 night award res.