Funny thing, I got tennis elbow from using a big old sqeegie and applicator combo at arms length, I forget what they were called now. My daughter is a physio and gave me an elasticated elbow support, it worked a treat right from the off. Have you considered training yourself to change leading hands? I Don't mean sack your foreman, just change to southpaw for a while. Most window cleaners are fairly ambidextrous, blading with both hands equally, it would only be aukward for a day or two.