If it tracks your calories burned for you, you can simply enter another activity.
As an example - I do Zumba workouts fairly regularly, but there's no Zumba category either. Plus, the burn will be a little different from everyone based on effort, weight, height, etc.
I wear a heart rate monitor when I work out with Zumba, and it gives me an average calories burned per minute (usually somewhere around 13). Thus, when I do my Zumba workouts, I will just log them as an activity that burns 13 cals/minute (I believe I often use stationary biking with very vigorous effort, and sometimes running or rowing when my burn goes up or down). It doesn't matter the activity - but the burn DOES matter. Just figure out your cals/minute and find the closest activity you can. Works for me!
Female, 31 years old, 5'4 1/2" tall
Starting weight 1/4/11 = 215.2 lbs.
Weight 9/19/14 = 176.6 (net: -38.6)
Last mini-goal: 180 lbs. REACHED! Reward - new sports bra
Current min-goal: 175 lbs.
Next large goal: 165 lbs. by 12/25/2014
Lowest weight: 156.7 lbs.
150.2 lbs. <--- Official "Healthy BMI" weight
Estimated final goal: 130-140 lbs.
"You don't have to change your life today. You only need to change your day today."