How do I move my world map sprites with a mouse button?

Hi, so I have a world map experiment made up of sprites to represent the land. I have it looping while using A & D to scroll left or right, however I would like to also be able to drag it with the middle mouse button while the sprites maintain their relative position to each other. I have no idea where to start with this.

I've had a look around the forums, but everything I have found seems to be about scrolling the layout rather than just the sprites.

Here's where I'm at so far.

https://www.dropbox.com/s/2ozf9i6tsav4k5z/Infinite%20Scroll%20Experiment.c3p?dl=0