I think a simpler way would be to parent a large solid to your vector shape and use that as an alpha matte for your text. I made a real simple project that should give you some ideas on how to do this.
I'm sure there are ways to control a mask with the position properties of another layer, but I think my way will achieve the same result and if you make changes to your vector position/timing, your text layer will update accordingly.
5566_textrevealcs5.5.zip
Johnny Cuevas, Editor
Thinkck.com
"I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work."
---THOMAS EDISON on inventing the light bulb.