[wildrhythms]

Airports do this all the time: Wifi is free for 1 hour, after that it's $X/hour. It's simply putting a "timer" on the MAC address.

[tinus_hn]

Then randomizing that address gives you a new hour every time.

[tombrossman]

Yes, tested and working for 10+ years now. Also works well if usage is capped/throttled after a certain amount and you wish to 'reset' the connection. Try not to abuse this on a shared network obviously, but if you have a legitimate need it's very simple.