Yes there is. Firstly, your application has to be available on iTunes.
When editing the design of your Pass, visit the Apple Design tab.
Then click on App on the left hand side and you are able to enter the iTunes Store country, and search for the app.
Select the correct app and click the Save button.
The app will now be displayed on the back of all Apple Passes. If the user has the pass installed clicking on the link will open the app. If the pass holder does not have the app installed when they click the link they will be taken to the iTunes Store so they can install it.