No, Apple blocked 10.3.9 and lower (including OS 9, actually) from their SU servers. If it were as simple as running SU on 10.3, I would've done it by now!

In fact, I might install 10.4, install FCP 4, and get the updates from there. Since 10.4 is still update-able in that fashion, I don't see why it wouldn't work?

c