Well, you should not outsource project - you should outsource people. Have a mix of inhouse developers who will cooperate with contractors. Force them to attend

Well, you should not outsource project - you should outsource people. Have a mix of inhouse developers who will cooperate with contractors. Force them to attend scrums, make them a remote part of the team. The difference is - you can use them for a period of time when you need them and then release the resources when they are no longer needed (fire them).