DAX has released a sample for full screen TV out with homebrew! :)
Yay!This is a sample to start the psp slim tv out from homebrew, using whatever cable (d-terminal has not been tested, but i think it has same code as component), and use it in full screen.
You start the sample normally, and then the sample connects to the tv out.
To use it in your code, you just have to replace the call to sceDisplaySetMode with the call to my custom function pspDveMgrSetVideoOut (which calls sceImposeSetVideoOutMode, which at the end calls sceDisplaySetMode), and be aware of the bigger resolution.
The good thing about the tv out, is that the resolution is really bigger (720x503 in composite, 720x480 in component), so it would be cool that video applications are ported to use it ;)