Cut away the dash? Not from my experience and certainly not what my install has told me. I wouldn't even bother taking the X5 to Bestbuy, go somewhere where you will find an experienced MECP certified installer.

There is a bezel made by a member on the board which you can fit a double din unit to, but there is no after market double-din kit available. It will take a bit of fabrication but definitely something an experienced installer can handle.