[MX04] Play external swf (preloaded) without button?

I have a main flash movie with 3 external movies, each loaded in a different level like so:

stop();
loadMovieNum("001.swf", 1);

This works great, all the movies are preloaded and waiting to be played. I can get them to play on a button click with no problems but what I really need is to get them to play automatically.

Basically, I have frames 1-3 load the external files, and would like frame 4 to play frameX of the movie loaded into level1 ; then frame 5 will play frameX of level2 etc. Without any buttons having to be pressed.

I currently DO have a button with this code:
on (release) {
_level1.gotoAndPlay(4);
nextFrame();
}

Is there any way to get the same functionality without the "on (release)" part?

I'm feeling really stupid here... TIA for any advice