No, is the simple answer. This is because the original Mellotron
instrument, which the M-Tron so faithfully reproduces, did not have it either. One of the beautiful things about the original instruments which M-Tron replicates was that it was often their limitations that encouraged artists to use them in new and innovative ways. The Mellotron, with it's 8 second sound length and lack of sustain had to be played in a fashion that was determined by these limitations, and that led to creativity. So we decided that they would be faithful to the original for the creative potential the limitations give. A partial workaround would be to MIDI remote control the Release slider, although the character of the sound changes slightly as the volume decreases towards the end of the Release time.