Pre loading external swf's

Hi

In my fla, I have a timeline with some basic animation. On frames 250, 500 and 750… I have 3 empty movieclips that loads 3 external swf’s.
Is there a way at the start of my timeline to preload the 3 external swf’s so when the timeline gets to frames 250, 500 and 750…they will play straight away?

I have to use external swfs (design reasons)

Cheers for your help
E