That footswitch will have to take a beating [MTBF?].  You can do it in the PitchFactor using two aux switches (which are easily replaceable).  {Note that it's also quite possible to assign KB0 – Mix and KB1 – Pitch Mix to a single Aux switch  –  see below}.

Use the HarModulator or H910/H949 algorithms to set up your intervals (e.g. 3rd and 5th).  You could even use HarPeggiator, Crystals, or even PitchFlex with the right settings.  Just intervals; no delays or extraneous parameters.  Diatonic or Quadravox will get you scaled-constrained effects.  Try that, "Impossible".

Under the AUX SW system settings:

KB0 (Mix)  >  TIP

MIN VAL –  WET:  0

MAX VAL  –  WET:  100

KB1 (Pitch Mix)  >  RNG

MIN VAL  –  A10 + B0

MAX VAL  –  A0 + B10

One aux switch alternates dry signal and interval.  The other aux switch alternates between the two pre-programmed intervals.  Barely more fancy footwork than the Impossible Pedal, yet more controllable and configurable.

You can also do this with an external MIDI pedal.  I use my FCB-1010 to alternate dry signal and intervals in a momentary (dry on release) configuration.  Another way is to use the EHX 8 Step Program plugged into the PF expression pedal input.

It looks like this Impossible Pedal is similar to the Whammy DT momentary function, except feeding two pitch shifters.  I read that it was based on Belew's Harmony Man technique.  Cool enough, but I'll stick with my Whammy / Ring Thing / PitchFactor combination to cover my pitch mangling needs.