Set individual transform keys
Need to key only the X position, or the Z rotation? This is a very basic script that pops up a little window having position X, Y and Z buttons individually, and the same for rotation. I left scale out of this since you'd have to assign a new controller for that to happen individually.
run the script from MAXscript > Run Script...
choose customize > customize user interface
choose "andy's custom" under the dropdown
for a button, just drag it to the toolbar where you want it. I've assigned the "create key" icon from the trackview to the button by default. You can change that if you wish. I thought that made the most sense.