You could use a thick ziptie to secure the QR lever to the fork. The drunk or causal thief would have to carry a cutting tool (cut zip tie), or a pliers or visegrip (unscrew other end of QR). You could even wire the lever to the fork, then solder the wire (so it can't be easily untwisted). Now the guy needs more than a pocketknife.

But the best solution is probably a theft resistant type of QR such as mentioned already.