For this, we definitely recommend several helpers! First, one light-weight person gets on the shoulders of someone else. Then, hold onto other people while the unicyclist mounts. When you get really good (we haven't gotten to that stage yet), you can let go of your helpers and ride along. When dismouning, remember: sacrifice the unicycle to save the person! The uni is not that important. The person riding on your shoulders IS. :)
Another option is to do piggy-back rides. This is a bit easier. :)
One thing we do with strong people who unicycle well is juggle balls or clubs while riding on their shoulders. If you're still wanting more challenges, you could try riding the GIRAFFE with someone on your shoulders (use a basketball hoop to get on). Good luck!