My favorite has been asking the team to set a goal and then choose a reward.
A fancy dinner, new headphones, etc.
Have them calculate how many commissions they would need to afford that thing. Then encourage them along the way!
You can also set smaller rewards along the way. "We'll get ice cream on Monday if we get 9 applications by Saturday"
Having your team create their own goal and reward that they purchase themselves creates excitement and ownership of the goal.