It sounds like ENA# could be pulled low on board by using a switch. Maybe one for each axis or individual switches. What would be the difference/reason in using ENA# vs. SLEEP mode? Not sure exactly what each is used for. But there seems to be these two options on-board.
I think one would still hold position, the other would not. And I think the newer boards no longer have the sleep option.
Mach3 2010 Screenset
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)