I'm trying to do this, but what if you booked the Cat 1-X award first, accepted whatever room they gave you for night 1 and then attempted to upgrade for the remaining cash/points nights? Is the problem that the system wants to automatically combine the reservations?

My other idea is to switch properties after my Cat 1-7 award night (Breathless Montego Bay) and then walk next door to one of the Secrets properties for the cash/points + TSU nights.

[Update: after booking a points + TSU award, I am waiting until the day before checkout to see if there is availability for a Cat 1-7 anywhere on the island and use it to extend my vacation and get another Brand Explorer property.]