i'm glad i'm not the only one that has run into that... i thought i was just unable to find the data anywhere!
My solution, was to put some script in the "feedhold" button, that activated a user LED, an output for external indicators, and then it "presses" the feedhold button...
I haven't actually run this on my machine yet, as i have other priorities right now, but... might be a thought for you!
*edit* The manual for M3, is MOSTLY the M2 manual, but refer to the customization wiki from the artsoft main page for your current LED's, Buttons, OEMcodes/etc.. they (and some of the functions that work with them) have been changed in the mach versions, and even within the M3 versions...
-Nate