masks are stricly 2d, and they can't use expressions to link a vertex to another layer or control.
crgreen.com does have a script that can do it, but you will need to re-run the script if you modify a point that is tracked by one of the vertices. and i'm not sure how it handles 3d coordinates.
motionscript.com has an expression that i have used to have the end points of the beam effect track the 3d layers:
http://motionscript.com/design-guide/threeD-corner-pin.html
the line is still a 2d line (no depth of field or perspective) but it will attach the end points to 3d objects as they move about.
Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW