Being a solid body made it a little bit easier as I had to shape up some timber pieces to go down in the mounting screw holes to act like spacers. I then drilled 2 holes either side of the original mounting screw hole in case I wanted to swap them out at a later date and proceeded to screw both PUP's into these custom made spacer/anchoring points. First attempt was too low and ended up dropping in a 6mm ply bit of timber cut to the exact shape of the PUP hole and then screwed down through that.
It was a right proper PIA, very fiddly, but the stripped back look was worth it in the end.
Not sure if you could pull this off on a ES type guitar and as I don't own one cannot comment.
Some alternatives that went through my mind were to use rose wood timber PUP mounting rings and cut the neck one to fit around where the neck meets the body. Like most things these are available on eBay and also Real Parts.