For purposes of safety having an in-dash can be easier to hide since you can simply push it in. However if you really wanna build it into dash, then I would suggest you build in a little cover for it. Hard to explain but basically when you need to use it you just push back the cover, and vice versa when you want to hide it. How this would be done with your dash I wouldn't know.
Probably be a bit simpler for people if they could seen a pic of dash.
also another idea @ sweet screen-hider idea