by Stephen Vickers.
An alternative to another checkbox might be to change the existing "Content-Item Message " checkbox into a select tag with options of "single item" and "multiple items". The former would be the default and follow the current workflow. The latter would send a value of true for allow_multiple and auto_create and skip the "Add External tool" page when activated from the activity chooser and bypass it on the return as well (however it was activated).