It's fairly easy to check if they are actually floating contact windows seeing as you already have the window handles. Within the callback loop you can simply call
GetClassName and
GetWindowText. Floating contacts have a class name of "#32770" (Windows standard dialog class) and a title of "Float".
The problem is detecting when these windows are created, your method of checking during the SigninReady event should be fine for existing desktop contacts but if you add any more contacts to your desktop they won't be affected by it until you next sign in, and I don't think you can detect when these windows are created (maybe you can with subclassing).
It would be much easier if Patchou implemented this into Plus!
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