You’ll need to provide a “place holder” URL in your application record first – by having a placeholder there, it effectively is the equivalent of a “boolean” saying “yes, my application can use callback-based OAuth.” The non-existence of that URL will imply that you only want to use out-of-band or xAuth forms.
No matter what value you do end up putting there, make sure you’re explicitly providing an oauth_callback value to oauth/request_token
