Why not use vector elements (logo, text, background, only people as PNG, maybe evn GIF in native resolution, not scaled in AE), turn off motion blur and effects, then export as SWF? Shouldn’t be over 50kB that way…
You CAN NOT use Add, Lighten or Screen to generate Alpha and render with Alpha. All blending modes needs underlying layer.
Luma Key and Unmult, however, are different story 🙂