Linux, disable alt+left mouse press drag

Hi all,
i've an application in linux where, for certain widgets (not all), i want to disable the alt+left-mouse-press drag. Reimplementing mouseMove (or even installing an eventFilter which manages move events) doesn't work cause this event comes after the widget is already moved. I thought the solution of reimplementing the x11EventFilter but i have 2 problems here:
1) I don't want this to happen for every widget.
2) This drag-move can be achieved on some linux systems by other keyboard-mouse combinations, which means i must focus disabling drag-move and not the mouse-press (which then starts the drag-move).

I've also tried to set the flag "x11BypassWindowManagerHint". This actually works but it has a side effect: The widget stays on top of everything (i mean on top of every application, not only of every widget of my application!).

Any ideas?
Thanx in advance

p.s. I've had also the same problem of resizing with alt+middle-mouse-press but i resolved it by changing the minimum and maximum size of the widget.