Step 1: book one of the most sought after bands
Step 2: release any song from their most popular album
Step 3: release more... wait, what happened to step 2?
"Licensing is hard."
Also, several bands debuted without their biggest songs or even any song from their biggest album. Heart, Midnight Oil, Journey, Bad Company, the Police... we just might not have noticed in those cases because the songs we did get were still pretty big, at least for the most part.
Considering U2 was long thought to be the band that wanted their own game "like The Beatles, only bigger!" I'd say it's a major get that they're coming to RB4 at all. And with Harmonix's promises of more tracks to come, you might see step 2 soon enough.