[capink]

You have two options depending on the action:

1. If the action supports scopes, you can do it by setting a scope in a manner similar to the post right above yours. You use template scopes, and start from the currently selected books and restrict down using whatever criteria you want.
   
   

   program:
       book_ids = '';
       for id in from_selection('id'):
           if $#my_custom_column then
               list_union(book_ids, id, ',')
           fi
       rof;
       book_ids

2. If the action does not support scopes, you can use the above template in the "Search Using Template" action. Just be sure to check the option "Template output is a comma separated list of book ids". And of-course you have to make sure the option "select all book resulting from template" is also checked