MJ polytools is close to what you need, but it is percentage based rather than distance. I am working on enhancing it now. I have it so you can do this via distance, and am working on getting it to take the resulting coplane created and making it a bevel. It is about 90% functional, but I am working on some bugs right now.
One thing that MJ doesn't do well is handle a coplane that goes around a corner. The inside corner on the coplane is problematic unless you prep the geometry beforehand. I have added a method that preps the geometry for a given selection also.
If I could just sort out a few simple selection issues and some scriptCtx stuff I think it would be very functional. Unfortunately, there are some limited cases where MJPolytools is goofy and hence my enhancements are goofy as well, but I am close.