Ask people to do a one-time serve to help accommodate the increased attendance or special event. Remember to never use the word "need" but instead use a word like "opportunity." You will find that many people are willing to help out for a special day or event.
Make it easy for them to serve. We have a five-step process that people go through to join our team that includes an application, reference calls, an interview, and background check, and orientation. But on this day, we simply do a sexual predator check, place them with an approved volunteer, and have them sign an agreement not to change diapers, take children to bathroom break, etc.
Place them with a "rock star" volunteer (click here for more info). Our key volunteers wear shirts that say "rock star" on that day. They model what it means to serve and share with the person the joy and spiritual growth they receive from serving.
At the end of the day or event, give the person a brief survey card and ask them how they enjoyed the experience. Ask on the survey card if they are interested in coming back and joining the team on a regular basis. We have discovered that up to 50% of the people will say "yes, I want to come back."
Follow up with them that week and get them started in process of joining your team as a permanent volunteer.
Try it...it works.