it is just an idea, but you could try
1, enable DNS
2, set up an IP list (ex: youtubeOK) of local IP addresses that you want to allow access to youtube
3, redirect UDP and TCP port 53 traffic to your router where source IP is not on youtubeOK list
4, set up a static IP DNS entry for *.youtube.com 188.8.131.52 and *.youtu.be 184.108.40.206
Possibly you will have to add a few other cctld variations of the name as they run under different domains in different countries, but it should be less work than IP hunting.