How do I create a 'guided' fill?

[titaniumapple]

I've got some text with a hollow border (or hollow 'stroke'), and what I want to do is make an animation that fills this border by following the outside of it (like if you injected a liquid into the hollow section, it would flow around it, that's the effect I want).

I've tried using shape and motion tweening, but it's just not working. I might be doing it wrong though, so if there's a way to do it quickly and efficiently, I'd love to know.

If there's a way to do it using guides and/or masking could someone post a tutorial on how to do it, because I've only just started using flash and it's over my head.

Thanks a lot