We did something like that. We used the in-law's address in BKK, but the reality is we were living at various different addresses around Thailand. We simply did not mention our other addresses; went back to BKK for the photos & police visit, and all was good. This lasted for about 12 months until we got a more permanent home, and then changed to a different office.
The thing is, they *might* interview neighbors to double-check your story. We had our neighbors all lined up (FIL has good relationship with them) but in the end, the cops just interviewed our sister-in-law and we were approved with no problem.
Make sure your room is all set up in the sister-in-law's house, with your clothing & personal items in case it is inspected.