My previous reply was mistaken – hopefully this is correct.
Input and Output Swell should do what you want, except that they only reduce level – they do not boost it. You could turn your amp up and then ride the pedal.
The Swell can be enabled on a preset by preset basis, or globally.
Note that the current value is not saved with the preset – the expression pedal is always the current swell value when enabled. The range is always from zero to full.