I decided on a low tech, push pull control for the water valve, I cant match the other buttons on the dashboard style so this option seemed the most discrete.
CBS sell these with about 1.5m of cable, its then cut to size & the loop on the end to pull the valve:
Push for cold:
Pull for hot:
I'll have to create some sort of label for it to get through IVA, I also need to double check those radiuses on that knob. Worst case I simply won't install the knob for IVA.