If you can't do this locally, I suggest just boosting with friends, as it's pretty hard to find people through matchmaking, as the GH servers now are pretty bare.
It doesn't matter what difficulty anyone's on (doesn't have to be Expert and also everyone can be different). So, just have everyone play beginner and that should at least make it a bit easier.
You'll be able to tell if you've missed it if the outline of the star on the star meter is no longer glowing.