Ability to switch out of cycles "Render Preview," mode quicker

A small request, but I work with a lot of large, complex meshes which take a LOOOONG time to build BVH for and transfer to the GPU. Every once in awhile I'll accidentally click the "Render Preview," button and have to wait something like 30 seconds for it to start rendering before I can switch back to say... wire-frame or whatever I was actually trying to switch to.

It would be nice if I could hit ESC, pause it, or still have UI control to switch to another viewport option without waiting for the build process to finish.