Horizontal scrolling of an MC based on the user's

I have been trying to figure this out for awhile…here is what I’m trying to do.

I have a strip of thumbnails in an MC that is quite long. I am masking this long strip of thumbnails so only a few can be seen at a time. I want the user to be able to move this strip to the right and left based on where their mouse is.

But a lot of the solutions I’ve seen have used the stage width to achieve this…however, I only want the strip to move if they are over the ‘active’ area…basically if they are over the mask area.

And then when it reaches the end of the strip, it would stop hopefully.
I’m hoping someone can show me a sample of this…or teach me how it can be done.
Thanks