I gather it depends if you have aircon or not. If you have aircon it's a big job because the air-con equipment is in the way and the dash has to come out. If you don't have air-conditioning installed, you may be able to get to the flaps and linkages to have a wiggle and free them.
I can't tell you exactly how to get in there, I don't have aircon but a garage removed my dash at great expense to fix a similar problem before I found out it was doable without so much dismantling. I think a bit of googling will find you some more information on this from people who have done it. Use the words r107, flaps, stuck - that sort of thing. This one for example: