Caching service usable for isp ?

We have an ISP with few thousand users which connect by PPPoE .

Each user has his own public ip .

We have central caching DNS servers and users transparently forwarded to them .

According to documentation , users MUST set dns search domain to everything work . If i understand correctly , if the dns search field absents then the os even does NOT request dns query _aaplcache._tcp . This part is impossible for us because there is no dhcp server .

Other parts of requirements seems ok and ready right now .

I want to know that is there any trick / workaround to transparently forward apple updates to our existing MacOS Server(MacOS Sierra Server 5.2) Caching Service in ISP scale ?

Note: Currently we have unofficial implementations like squid but we want to move to official ways for better performance and bandwidth saving .

Thanks