The way I understand is that the 4-button block consists of two switch modules - upper and lower. Thus solo switches are not available.
View attachment 109682
So possibly you could replace your "Windscreen heater (only)" module with "Wlan/Bluetooth + Windscreen heater" -module.
It seems that for lower module available are only either "Regen" or "MODE" modules.
I'm not sure what's the Wlan/BT was meant to do. Possibly related to a special versions of T6.1 - VIP Bus or taxi??
No good ideas what the MODE was meant to do.
I guess you could you use any of these "new" ones as general purpose switches. Most likely there is no wiring present on van's side.
Anyways, I haven't had any of these in my hands - so no responsibility accepted