I am installing yet another double vanity. Can I put two 45s in my drain pipe in order to bring it over a few inches to the left. That way when I install my double fixture fitting, I don't have to put as large of a hole in my 2x4 since as is now the hub will sit in the stud. As
Yes, especially since if you use the CORRECT fitting, it will be too wide at the branch connection to fit next to the stud even with a larger hole. AND do NOT forget to install a cleanout fitting below the "back to back fixture fitting" so the line can be cleared if it plugs up.