Here’s something to experiment with.  DELAY at maximum, reverb at minimum, plenty of LOW-, HIGH-, and MID-DECAY.  The pitch shifters mirror perfect 4ths, and PITCH-DECAY loops everything around at 100.

HotSwitch programming: Switch LOW-, HIGH-, and MID-DECAY to 0.  That leaves a touch of ambient reverb (nothing else).

The expression pedal here sweeps through the narrow range of PITCH-DECAY: 100, PITCH: FREEZE, and PITCH+VERB: FRZ.  One cool performance technique is to adjust the upper range to ‘just barely’ on PITCH+VERB: FRZ .  Then you can use the majority of the pedal travel between PITCH-DECAY: 100 and PITCH: FREEZE.  Only the top 5-10% of the expression pedal will kick in PITCH+VERB: FRZ.  Makes it easy to selectively add to (and edit) the ‘frozen infinite’ background.