Your best bet is to just buy a replacement dash piece. Do all your fab on the spare dash piece and save the OEM one. Sell the car, just swap them back out.
If you try to make it overhang like that it will stick out like a sore thumb. It will look out of place.
If you still want to do it though, I would not use velcro.
Pics would help for sure. Also keep in mind, if you are planning on sticking things into deep pockets to keep it there, it wont look so nice when you remove it (scratches, warping, paint flaking).