You didn't read it all ("Rather than wasting time going back and forth with the local bank branch, we decided to go directly to the Bangkok Bank HQ in Silom. (Thank you for previous suggestions from this forum about going to Bangkok Bank HQ!")
A lot still unclear but I guess there's still time. Will you be able to check in for a flight to Thailand without having completed it, or is it only checked at passport control in Thailand? Can you complete it after arrival, like you could with the paper TM6?
I've usually done it the other way round. Get the new Extension, then my HR officer goes to MOL to get the new WP stamp (without me having to be there!).