Prims that can move betweeen island?

I am trying to make a script that could move avatar, once he is sitting on them, between islands as well as within them. It is easy to do for an object using llSetPos but it it only works within one island. What is a way to do same thing, but be able to move between island as well, and specify coordinates in one island, and the other.

These links should get you on your way to doing this:

Global Coordinates:

http://lslwiki.net/lslwiki/wakka.php?wakka=globalcoordinate

llGetRegionCorner():

http://wiki.secondlife.com/wiki/LlGetRegionCorner