I think in your case you wanted Num Lock and not Scroll Lock.
But I'm not sure that would work.
As a test you can create a script like this:
xset led named "Num Lock";sleep 1;xset -led named "Num Lock"
give it 700 permissions and run it. If it works, it should turn the Num Lock turn on and then off.
Testing it here, it works when I use Scroll Lock (the LED blinks), but it doesn't work with Num Lock (the LED stays on). YMMV.
If you can figure out how to make the script work then you can worry about the keyboard shortcut.