Tricky RandomBG function: Query

I have came across a tricky situation to find a code for:

The following is a code i have generated for displaying random frames when a movie loads. (this is contained in the onClipEvent load)

function randomBg() {
//generate random BG based on random frames within the MC
randFrame = random(3)+1;
bg_graphics.gotoAndStop(randFrame);
}

stop();

There are 3 movie clips placed on each frame of this movie clip (bg_graphics). Each of these movie clips has a short animation that i want to trigger somewhere later in the script.

Q: How could i target this randomly generated frame/movie clip to gotoAndPlay frame 2.

Do i need to generate an ID name for this bg_graphics moive clip?
Please help, anyone???

Cheers
Peter.D