There was a script from nabscripts named "maskPointsExpression.jsx" that did what you wanted but alas his site is no longer online, but...
there is a similar script that should do what you want, named "Connect_Vertex_to_Point.jsx ", here:
http://www.crgreen.com/aescripts/ie/
Just download the jsx file and drop it into you AE Scripts folder, then open AE, and you find it under File>Run>Script...
I have no expertise or detail on the second script as I've never used it, although the description fits your problem.