I was looking at this place at making some 16x10 wheels.
According to most offset charts I've seen the closest backspacing that would work for a Subaru is 7" which is the largest they offer. Their wheels are mainly made for cars with negative wheel offsets. 7" would give the wheel a +37mm offset, according to their charts. That should work but it may require some spacers and the that's definitely going to stick way outside the fenders in the rear. The wheels are cheap, like $260/ea and only weigh 14.9 lbs in 16x10. I would not recommend using them on the street however, they would likely not last very long, but a lot of guys seem to use them for road racing.