The following should get you a good approximation, but there may be better procedures out there:
Take the current WAR total for the team. Divide by games played. Multiply by 162. Then add 49. Then divide by 162.
49 is a number I generated in my own research. I often see a slighlyt large number. Awhile back I remember looking into how many total wins WAR generated and compared that with 2430, which is the total number of games won if every team plays 162. Subratcting total WAR in the league from 2430 generated about 1470 wins that were unaccounted for, suggesting that a replacement level team would win 49 games.