There are 3 star power paths on We Will Rock You that work for the solid gold easy action achievement.
Activate at 1/2 full (ie 2 sections of white notes) and 3/4 full (ie 3 sections)
Activate at 3/4 full and 1/2 full (same as above just other way around)
Activate at full and you pick up the last 1/4 on top.
You do not want to activate at 1/2 and 1/2 as this means you don't get to use the last 1/4.