Has been asked for a number of times but isn’t possible at the moment due to the way Slate works (it’s basically slapped on top of everything at the end). There’s no 3D Transform or any 3D rendering capability at all in Slate. It’s just marked as one of those “we’d like to, but it’d take a long time and be very difficult” kind of tasks.
The only current solution it seems is to use Render Targets in another hidden area (which is kinda sucky). I too would love to see this believe me!