I too would like an update on how to properly implement this workaround.
The ajax handler and coupon logic code in functions.php is in place, and in my case I added the jquery in the same page as the form. Unfortunately nothing happens when the coupon code I created is applied.
Perhaps is due to the latest version of woocommerce not being compatible with this solution, or we are missing something during set up O_O
Update: Silly me, my jquery needed to go in a separate file which then needed to be called from functions php. Works now 