That tech you outlined above sounds very very similar to something I learnt from Mark Barlow in Akayama Ryu.
My personal thing for boxing attacks - follow and ride his movement and apply kuzushi. This however calls for an uncanny ability with distancing and timing (which we tend to practice a lot from dealing with jabbing tanto attacks in tanto shiai training). What has worked best for me is to not even go for the arm initially, as the other hand tends to get you as he won't stay there while you attack it and go for kuzushi or technique. Most boxers I know will step back a bit or turn to get you off of them (open space) and then quickly come back in with a punch.
Atemi waza (as in Aigamae Ate or Shomen Ate) can be launched as quickly as any punch and used instead to throw. This has worked best for me, especially when the boxer is recoiling from the jab. Timing and strong entry though is key.
Second option would be to use reactive kuzushi (on the retract of the jab) to control the arm or body with any sort of strong entering technique. In this option you are using the energy of the recoil to help you move into the boxer to control the arm and get kuzushi. Simple options that come to mind are tenkai kotegaeshi, tenkai kotehineri or sumi otoshi. The key here is to enter deeper than where the Boxer has attempted to stop when recoiling his punch, else you just run into the other hand and get creamed. Kuzushi is key.
Just my 2 cents.