Hmmm... there appear to be quite a few different 3 bolt cleat styles, but generally not Shimano compatible.
It looks like IQ2 is making an a pedal spindle adapter power meter.
https://www.iqsquare.com/onlineshop
This might be one of the few ones that would be compatible with 2-bolt cleat types.
One issue, of course, is that it will naturally increase the crank Q-Factor by a bit. However, the size may be small enough that the shoe could overhang it a bit, if the spindles could be shortened or cleats adjusted to compensate.