Agree the pocket thing sounds horrible, I was not even considering this an option. I would only use two Petrels if they were wrist mounted. Kiss confirmed today that they can make the second cable the correct length.
As for the cable getting tangled in bungee or B/O's I'm not to sure how this would differ from the regular left side computer. Having a computer on the right wrist would not very any different than the left. Also my other unit is Triton with two Petrel's I used with the same Xdeep harness, normal loop bungees, and dive it often with 4 B/O's and never had any tangling issues.