I'm taking a look to see if I can pop it out from the engine code.
Right now I let the engine render, and then I copy the framebuffer from the HDMI over to the framebuffer for the TFT (standard /dev/fb1, but I have it so you can change it if that's not the case). The framebuffer copy code is currently called in Engine->RunFrame.
However, as I think about it as I type this, I could potentially just extend Application and stuff the call in there...that sounds like a much better option actually.
Thanks for the thinking point
EDIT: I should clarify a bit, the TFT display communicates over SPI, and so it doesn't actually have access to the GPU (so no OpenGL). Hence the render has to take place on the GPU and then get manually copied over to the TFT framebuffer. By handling it in the application doing the render, I can make sure that the framebuffer I'm copying from isn't being currently written to.