Stopping a loop/playing movie clips within one

Hi guys I have a movie clip on loop (refer to this post for my .fla -http://www.kirupa.com/forum/showthread.php?t=191373)

I have some masking mc’s I want to play within the loop (but not have it loop, just play at a particular frame and stop)- how would I go about doing that?

I’m so stuck, any help would be greatly appreciated!

Thanks!