This is not possible. BTT can trigger after you copy something, but not before you paste something.
(E.g. see Paste clean links from clipboard - #6 by Andreas_Hegenberg )
Making the clipboard content available as an advanced trigger condition is a good idea. I think I can add that with one of the next versions.
For most trigger types the "Use Apple Default Or Do Nothing" will do nothing. It won't help you with this. However if you want you can send the cmd+v shortcut at the end of your action sequence instead of using the paste text action.