I note that dsaul's caliper is mounted about 10-20 degrees clockwise compared to guy's. The entry angle of the cable need less bend and the adjuster is higher up off the stay too. As I look at guy's caliper mount/dropout it looks like the mount was added to the dropout and the top of the chainstay filed a tad for a flat fit. If careful cable routing doesn't work out perhaps a custom adapter plate that moves the caliper up, back and rotates it a tad too could be made. But I would experiment with a test cable and zip ties first.

Does the cable run have another adjuster, other than the caliper located one? Using a simple casing end cap (that has a snout that would enter the adjuster threaded hole) might get you a few mms of added clearance. Have you tried a V brake noodle? There are various angles of curve as well as flexible types. I also thought about a pulley type of thing but thick cables running around a pulley tend to add more lever pull slop feel. Andy