I've done it in sedans before (mainly Ford Crown Vics, they have the room), using this type of equipment:
http://www.galls.com/shop/viewProductDetail.jsp?item=VE099

It needs a base that will mount on the floor/transmission hump, so look at:
http://www.galls.com/shop/viewProductDetail.jsp?item=VE115

I don't see why you can't get a local welder to make you a similar rack, or you could buy one. Check Yellow Pages for the radio shops in your area that deal with the local FDs & PDs, or the city highway garage. These things get replaced when the cars & trucks get changed to the new year models. A used mount might be had for free, or very cheap.

My current rig is in a backpack. Can't see the screen while driving, but very stealthy. (One of these days I'll get the page posted.) I've been thinking of going to back to a mount like the above for my current vehicle. They are convienient.

Cheers,
Thorn