Hello Kilgore Trout, while browsing the forum today, I came across your post and maybe a late response can help you if you still have this problem.
1/ assign the only note to be triggered on your sampler (i.e. root key/low key/high key = E2)
2/ insert a MG2 “sustain” midi machine with the option: Forward CC64 to instrument. You can assign a different CC number.
3/ That’s all !
Play E2 then press MG2 sustain pedal on screen. It keeps playing the sample till the end unless you release it, while you keep on strumming.
For more convenience, I use a footswitch that can be latched or unlatched according to need: if you want to play whole sample, only part of a sample or loop several times.
I use (on pc) a free sampler called Shortcircuit by Vember Audio.
In a MG2 patch, a dozen of samples can be triggered all together or separately.
More on settings in my post Gear, Wishes, Works