I think it's always nice to send them an invite, just as a courtesy, but it's not a must-do.
You can call them after the invites go out and let them know that you don't expect them to travel a distance, but that you just wanted to extend the invitation to let them know about the shower.
Just remember that they still may send a gift even if they don't come. If you do get a gift from them, be sure to send a thank you card.