Trying to come up with a way selectively degrade performance for certain domains.

I don’t want to block legitimate but inappropriate domains, but am looking to make them excruciatingly slow or frustrating (eg intermittent, etc) to discourage their use by users on the network. Any best ideas on what level to be doing this? Router/ DNS, Firewall, etc? Been looking at QoS but it seems to be protocol/source based.