I think you have to use the unofficial SDL libraries to enable opengl the way you described -> http://dl.openhandhelds.org/cgi-bin/caanoo.cgi?0,0,0,0,19,521
then you can make a call like:
SDL_SetVideoMode(800, 480, 16, SDL_OPENGLES)
Alternatively you can use EGL with the normal SDL libs, heres...