firstly, we actually do recommend you configure clients to use the proxy. There are several ways this can be done without having to go to each client.
You can't intercept port 443 to the HTTP proxy, since the client expects to negotiate TLS/SSL straight away as soon as the connection is made. You could create a new web proxy on port 443 with SSL in the binding policy and intercept port 443 with that, but you'll get certificate warnings on the clients for every site.
So the only real workable solution if you want server name for https surfing is if the clients use a proxy.
Ways to automate:
1. Active Directory Group Policy. You can use AD group policy to force clients to use the proxy.
2. Proxy auto-detect. IE has this on by default. It uses:
WPAD DHCP option (option 252). You can add option 252 (string) in WinGate > Monitoring > DHCP > Definitions.
in WinGate DHCP server, add an option for WPAD under global options value of http://wingate/wpad.dat
If you're using another DHCP server, you can add the option in there instead. Basically the client just needs to resolve to WinGate's IP and make a request for /wpad.dat. WinGate will auto-create this file and serve it back.