Theoretically that’s possible, though not within the MODEP UI, and can be a bit difficult to get it right.
You’d have to install pure data in the MODEP image and configure Pure Data to use JACK for the backend. Once PD is launched, you’d have to make appropriate Jack connections so it goes to the speakers (or it should even be possible to make it go to some effect in MODEP) using command line tools, or set up a GUI in the image and use qjackctl or patchage to do that.