WiQuery: positioning a dialog when reusing it

In my application I am using WiQuery's 'Dialog' for a global page
dialog that gets constructed in my page base class. Each time I want
to show a dialog I embed a different panel in it and then show it.

Usually I would like to display smaller dialogs that fit on the screen
using WindowPosition.CENTER while for larger (i.e. longer) dialogs
WindowPosition.TOP would be more appropriate.

Now I see that setting the window position on the already constructed
Dialog object does not have any effect, the only way I can actually
set the position is by setting the position after construction, i.e.
before the dialog gets rendered for the first time. I actually found
this by trial-and-error, and the (rather terse) WiQuery documentation
does not give me much more of a hint.

Thus asking you - is there a way to reposition a reused dialog? If
yes, how? It seems so weird I did not find anything on this because
this requirement seems fairly typical to me...

Cheers,

Martin