Advice needed - Mariss' e-stop circuit

I am building a power supply using Mariss' servodrive e-stop circuit,
which is in the files section of this group.

http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/A%20Servo%20E-
Stop%20Circuit.pdf

I would like to add an on-off switch to this circuit. As is, the only
way to turn this circuit off is by hitting the e-stop switch or
unplugging it. I am wondering if a momentary-off-momentary switch
could be used? Since both sides of this switch are normally open, the
side that serves to interrupt the current to the relay's coil would
need additional components. Would a switching transistor work here?
If so, how should the circuitry it be set up?

I realize that I could easily use two switches on the power supply's
front panel; a SPST momentary NC switch and a SPST momentary NO
switch, but I am curious about the above mentioned option.

Any ideas?

Thanks,
Tom Murray