When I started living with my common-law partner in Brazil (January 2015), I was on a tourist visa so I couldn't get my name officially added to things until I got my permanent residence in the country, which was about 5 months later. Additionally, we were living as subletters in a house with other people, so my partners name wasnt even on the lease. So to show proof of co-habitation for the first five months, I included notarized declarations from the lease holders saying we had been living there together as a couple. I also included my plane tickets and passport stamps showing when I arrived, and photos of us together.
So far I haven't had any problem with just including this information; however, I also included other documentation from after that period including joint lease, bank account, Brazilian statement of common-law, PR issued on basis of common-law Union from when my status changed in July 2015.
Anyways, my point is I think it could work for you, but try to get some type of official document if possible. Also if you can get mail addressed to you at that address, or even better, addressed to both of you at that address that could help you as well.
