I've been trying the surface blur filter on a copy of the shot, blended it with 50 fill and then used that to merge it with the original again at 50 opacity to keep it subtle.
In the end the result might not be too different from high-pass blending.
I'll check out the filters suggested. Those might do a better job.
This guy has a great tip starting at 9:50 about how to use the high pass filter and blending modes, then gradually increasing sharpness by copying the filtered layer repeatedly until you get the desired effect. What you are doing reminds me of this.