How about a little interval (heartrate range 50-92%) I call it 3,4,5, and this is how it should be done!
Start class off with a 3 minute steated climb (60-80 RPM). Do a cadence check so that thaey know where they should be. Next go into a 3 minute standing climb. Then do 3 intervals of 30 second sprints, at a sprintable resistance, and 30 seconds recovery. Ok sounds fun now do 4 and 5. The sprints can also be performed in a standing position, the key is cueing. Depending on the Skill level of you class you can do a recovery set (heartrate down to 50% of max) in between the last 30 second recovery and the next seated hill climb. HAVE FUN!!!