You have several options--some of which only work with FileMaker 11.
You can create a separate layout for printing that uses a different portal setup and/or relationship.
You can add a "show all" option to your drop down--how you implement that depends on whether you are including the field in the relationship or if it is a part of the portal's filter expression (FileMaker 11 only).
A third option is to create a list style summary report based on the portal's table. This avoids limitations encountered with sliding portals and portals that can't display all the data when there are too many rows.