You can't import a form but you can create custom lien wavers to print at 3-2, 3-7, or for vendors. The one that exists for the vendors uses calculated fields from the set to pay window so they do have to be printed before you issue the check. Otherwise you can customize the form to include a pop up window where you can add the necessary information.
Please contact your Sage Certified Consultant for help with customizing forms (as report writing is not supported by tech support). There are also classes on Sageu.com to learn how to do them yourself.