you can take over the MQ 1 month before you are married but you arent legally allowed to live in it until you are married (unless other half is pregnant and then the rules change a bit), you wont pay for both the singlie accom and the MQ as you can only be charged for 1 at any time. (err allegedly)
Find an empty MQ, break in and install your potential partner in a a squatter. They won't know what to do so chances are you will get away with it. If you are lucky you might even get away with not getting married.