So, I've learned a little more...
If you are on shared hosting, some of the instructions (such as groupadd) will not work from the shell.
I suppose it might be possible to switch to a VPS, wait a day, do the install, and then switch back to shared hosting, but dang, I dunno.
I would be happy as a clam if it was added as a one-click, but someone from Support said that there are no plans to add any more one-clicks (sad face!) soon.
However, I would ALSO be pretty happy if there was a step-by-step for installing it yourself. I don't mind doing that -- I just don't know enough about the system to know what I can or can't do and what may or may not screw things up.