Ok, turns out this is a non-trivial process.
Once you've created and signed packages, you then create a custom channel and use rhn_push to add the packages.
While you're creating the custom channel, there is a slight bug with the interface. The input box is one character too short to accept the output of gpg --fingerprint, so you need to paste the output, then erase the additional space that gpg puts in (between most blocks, there is one space - between one set of blocks there are two) and type in the last character of the fingerprint now that there is enough space.
This gets the file _into_ satellite, but I'm still working on installing it to satellite managed servers.
You have to add the newly created custom channel to the system, and then the rpm is eligible to be installed. However, you still need to get the key you created out to the custom systems. That's the bit I'm working on now.