I think, you cannot.
Other than transforming your SWF with some tools out in the wild to new code. (I have no suggestion at hand what tools you should use. I'm out of the Flash/SWF thing quite a bit.)
Or do the thing in Adobe Flash altogether.
And using ActionScript 3 to get the code minimized.
I haven't created SWF for some time because I think it's a dead-end technology. But I remember that InDesign produces particularly large, unoptimized SWF files. I would create it in Flash Professional, and ask in the Flash forum about file sizes.
Hi Uwe, hi Steve,
i know that Flash Professional is the software for creating swf-files, but we work mostly in InDesign and the new features gives us the chance to work with it.
I make a test in InDesign with a blank page and eport it to SWF and i get a Filesize from 124 KB. The Export to fla is not bad, but the transport of the animations isn't correct.
Secondly i bring down all used illustrations to a small size with Photoshop and the Export for Web with a maximum size of 30 to 50 KB but it makes no sence to the result.
Doing that in ActionScript 3 will help a lot to reduce file size. Just a small overhead to your image file size. Maybe 6 to 12 KB only.
You'll need someone to script that, though…