My heater switch has snapped, and am trying to remove the heater panel to get at it without breaking anything.

Ive removed underfacia trim (where cigarrete holder is). This got me access to the screws for the heater panel, panel loose at bottom still not coming out.

Im guessing from the Doblo mechanics guide i have that the problem is the central air outlets need removed next.

or does the whole dash need to be removed ?

I had a knackered "burned out " switch. I've still got the dash hanging out ready for the new switch.
This is what I did : I took the bottom off the steering column off so i could get to the rest of the screws that holds the plastic middle bit under the gear stick. With that away there are some screws that one can see at the bottom of the center dash. you then need to pry off the two air vents that are above the heater control. this will enable you to see the hidden screws that hold the middle cover.
I found that i still could not get to the heater switch due to the control cables. So I took of the glove compartment off and took off the hot/cold cable from the heater box. This just gave me enough room to pull the heater control out so as to get to the switch.
Sorry I never looked at the date of your post.
PS I used a screwdriver bit on a socket to undo the switch .
I hope this helps.