If you add CH1 and Ch2 (either internally -- don't know if that's possible -- or externally by simply "T"-ing them together) and output a square wave on one channel and a triangular wave on the other and adjust the same frequency on both, it shouldn't be difficult to adjust phase and amplitude in relation to each other to generate any sloped square that you like. Of course, this would require both channels so if you need the second channel for something else, this isn't possible. I'm not sure if some modulation function may be configured to produce the same result.
Cheers,
Thomas