You can do it by modifying the 1024.set using the Mach3screen software. When you open up the software, load the 1024.set from the mach3 folder. Go to screen 50 on the top of the program and double click the jog mode button. There you can set a hot key for that function. For example crtl j or any other hot key that mach3 is not using. Once your done, save the file and then reload mach3 with the new screen set. Hope this helps.
Regards,
Raul