I was looking at subst, but it doesn't really do what I want it to.
What I want is to take the co-ordinates of the Mtext insertion, subtract the mtext height from the Y co-ordinate and use this value as a point to copy to.
What I did, was use the list command to build a new point list to use as a co-ordinate, but I think there must be another, better way to do this.