Maybe helping to excuse my mistake, I think I found a workaround for your original request :
In a DAW, set one sample with the atttack of the sound, another with the looped part.
Make it a 2 slices sample with Octachainer.
Play it as a looped slice, LENgth = 2.
Only the second slice is played looped. Have to check again.
Edit : Apparently you have to set a loop point at the beginning of second slice for this to work…easy, just turn loop knob to the left.
Too tired to elaborate, I know it is not clear, but it seems a really interesting possibility.