I know you can send MIDI Program Changes that are attached to clips. I’m pretty sure that it will send them when the clip starts.
So, you might need dummy clips that have program changes. There is a setting somewhere that has the resolution for changing patterns in the OT, so, you could queue, or, switch on demand. But, Program Change is usually a slow command for MIDI, so, “on demand” might be pretty glitchy.
Edit: Since the OT has 256 patterns and Program Change only deals with 128 locations, you might need a Bank Change CC sent, which is either CC 0 or CC 32, depending on the gear. I’m guessing it’s 0, since the OT won’t send CC 32 as bank change (I have a ticket in for this at Elektron).