Adding to mistercharlie‘s suggestion: CHOP is a useful UltraTap parameter, and its SPEED can be mapped to an expression pedal. Here’s one example, that you can modify to fit your needs:
https://www.eventideaudio.com/community/presets/brock/slowgear-tremolo
That said, the same can be done in other algorithms, like TremoloPan or TremoloVerb. Maybe even the Undulator algo. Of course, TEMPO should be ON, in any case.
