My wife and I recently bought a new house, and in the finished basement, there's a bedroom with two ceiling registers. The home inspector noted that both registers were return vents, so since there is no way to shut off the airflow when the A/C is on, he recommended installing two or three way registers. When I returned home with a pair of two way registers, I soon determined why one way registers had previously been installed. The duct size is suitable for 10" x 6" registers, as if I selected anything larger, the portion that opens/closes when the louver is pushed will not fit in the duct. However, the issue with this size is that the ends of the registers, where the holes for the screws are, do not extend to the ceiling; instead, they're just at the edge of the duct, so there's nothing to affix the register to. The previous homeowner (remodeler) likely bought the one way registers so he could use a larger size that extends past the duct to allow it to be screwed into the ceiling but without having to worry about the portion of a two or three way register that needs to fit in the duct itself.
Does anyone have an alternative way of somehow affixing these registers so they're secure enough that the louver can be used? Thanks in advance for your help.