<p>We have a service that has some settings that are supported only over net.tcp. What's the best way to add another endpoint? Do I need to create an entire new host?</p>

A service may have multiple endpoints within a single host, but every endpoint must have a unique combination of address, binding and contract. For an IIS-hosted service (that is, an .SVC file), just set the address of the endpoint to a
relative
URI and make sure that your Visual Studio or wsdl.exe generated client specifies the endpoint's name in its constructor.
See also the MSDN article
Multiple Endpoints
.