Default to FREEZE, ‘sample’ the note playing, then snap back to FREEZE.

But when you release the switch determines the FREEZE output level(s).  FREEZE mixing by tap timing.

• Rapid switch release, and you’ll capture a stronger signal; closer to your note attack. 
• Wait longer to release the switch, and you’ll capture some of the note decay.
• Switch during muted input to ‘erase’, or freeze inharmonic transients.

If LAYERS are the focus of a SE+ simulation, it’s better to break out the expression pedal.  Yes, that brings a BLACKHOLE-ish reverb component with it.  A simple swap of the Heel & Toe values – with the change to expression pedal – turns that preset into an ambience generator with full-range mixing.

Expression Pedal Heel:  DECAY  0.5 S

Expression Pedal Toe:   DECAY  FREEZE

The DECAY default was increased to 1/2 second.  That, along with the larger SIZE for thickness, produces a small room ambience.  It also smooths out the abrupt contrast between 100% FREEZE, and 100% UN-FREEZE.

Moving the expression pedal away from Heel, the room reverb expands.  Depending on DECAY & SIZE interaction, you’ll begin to add true ‘LAYERS’ around 8 – 10 – 12 Seconds of DECAY.  In the area closer to Toe, it hits the ultimate LAYER generator [INF].  That’s the equivalent of an SE+ LAYER knob set fully clockwise.

Just beyond that, at fully Toe … FREEZE.  One smooth technique is to hover in the upper half of the expression pedal throw.  Notes are blended between INF, FREEZE, and the mega-seconds reverb area.  When you need to pull back on sustaining output & levels, just ‘pull back’ on the expression pedal.