Lock for metal casement window?
 

I have a single-pane metal casement window with a "T" crank. The vertical locking mechanism works fine, but only locks the window in a closed position. Is there a supplemental lock I can install that will permit the window to stay open slightly? The metal frame is very narrow (house built in 1954).

I've searched around and not having much luck.
Thanks

Easiest way to limit access would be to just remove the handle. Those old casements didn't move too much without it.
Ron