SGX with multiple framebuffers on Beagle + Linux?

I’m a newbie conc. SGX/BeagleXM + Linux and ran into the following issue:
(sorry - probably a bit off the actual SGX scope, but experts maybe have a quick hint for me? Embarrassed)

I can run one SGX GLES app with the NullWindow system and see it ending up in framebuffer fb0.
Is there a straight way to start a second SGX app in parallel and target it to a different framebuffer e.g. fb1?
(This way I could use the display subsystem to have both buffers merged in a layered way to the display, e.g. with alpha.)

Or will I need to use windows systems like X11 or QWS - and if so will they utilize multiple framebuffers (or simply blit the surfaces internally)?
For my use case fullscreen apps are fine and I’d like to avoid any overhead of X11 or QWS.

Thanks,
Volker