Progress report:

I took the screw out of the back of my Shimano Ultegra triple front deraileur and evenly spread just the rear portion of the inner and outer cage about 1/4 of an inch total. I inserted a 1/4 inch nylon spacer and a longer screw. In my first trial ride today, the chain rubbing is almost gone over the full 50/34 front to 11/32 rear. I'll test it over 100 miles this weekend to see if the chain jumps or jams.