You could try creating a
.Xmodmap file with
keycode # = Delete. Use
xev -event keyboard (you'll likely need to install
xev) from your terminal, it'll pop up a window. Press the lock key once while having the window focused, and you should see KeyPress and KeyRelease events in your Terminal. Look for the keycode in the event, replace
# with the number, save the file and restart.
Example KeyRelease event:
KeyRelease event, serial 28, synthetic NO, window 0x4800001,
root 0x1e2, subw 0x0, time 42279132, (15,111), root:(2646,491),
state 0x0, keycode 41 (keysym 0x66, f), same_screen YES,
XLookupString gives 1 bytes: (66) "f"
XFilterEvent returns: False