There's a few flaws with your plan.
Using an IP instead of a hostname
A network admin can still perform a reverse lookup based on IP. The common tool to do this is via whois. The returned site might be exactly correct, but it will leave some clues to the admin.
The HTTPS header will prevent the content of the request from being disclosed. However, the destination IP needs to be known in order to successfully route the request. Therefore, it is impossible to mask the destination IP.
If the network admin uses a Certificate stand-in, your machine establishes a TLS session with a proxy and then the proxy establishes a connection with the destination website. When this is done, all connection information will be available to the network administrator.