CTRL-ALT-END on numpad doesn't work

Anyone seen this before?

If a user tries to unlock a VDI session (windows XP) using a keyboard without END button, he can't unlock.

This should work with Numlock turned off and pressing CTRL-ALT-1 (=end) but nothing happens.

I tried this on a normal keyboard, and indeed the CTRL-ALT-1 combination doesn't work.

Is there a workaround for this?