Converting relative into absolute Coordinates

Since WinMove seems only to work in absolute coordinates I wanted to convert my relative coordinates into absolute ones.
The problem is that I can only think of one filthy way to complete that task and that involves MouseMove. For example:

Opt("MouseCoordMode", 2)
Winactivate([$WorkingWindow)
MouseMove($X,$Y,0)
Opt("MouseCoordMode", 1)
Local $abs = MouseGetPos()
Opt("MouseCoordMode", 2)
WinMove($Window, $abs[0], $abs[1])

Can you help me out with a better solution?

EDIT: Thank you very much. This is just perfect.