So here's how I was able to get ghosts for the mountain goats league.
1. Go to the league's page where stages are listed. Each active stage should have a "copy" link in its upper right corner. It shows up in blue in my browser. Click on the link to create a league copy of the stage. Do not click the larger blue emblem on the lower right corner. That link will create a league ride you can't modify. I have *no* idea why they're different, just that they are are.
2. Head to your scheduled sessions and find the ride. Note that you may have more than one in your scheduled sessions. You have to find the one you just created. In theory it'll be near the top of the list of your scheduled rides since the "copy" link will schedule one for the current date.
3. Add ghosts & bots and hit the "Edit" button. You can also remove the splits that resync your ride somehow ultimately resulting in a shorter ride than expected, then some kind of adjustment from bkool after the ride is complete.
4. Ride
Now what's damn strange is this works for the mountain goats league, but it doesn't seem to be working for the mountain moose league. I don't know if it's a function of the way the leagues/groups are set up or a function of the ride itself. The leagues share a couple rides, so I'll be able to test if it's the ride or the league tomorrow when City Creek opens up for the goats.