Transparent model on top of a background

Hi,

I am building an application, that displays a 3D model on top of a background image so that the model is partially transparent and therefore the image can be seen as well behind the model.
How can I achieve it?
Crrently I am setting the background image with the AIS_View::SetBackgroundImage method.
My first idea was to make the whole model partially transparent using the AIS_InteractiveObject::SetTransparency method, however this way the hidden parts of the model could also be seen, which I would like to avoid.

In some earlier forum post I have seen that it is possible to display an image using an AIS_Shape by setting the image as its texture. Then this shape could be placed on the overlay layer so that it is always displayed above the 3D model. If the texture is semi-transparent then I guess that the model will be visible. My only problem with this solution is that this way the image will be faded everywhere on the screen due to the alpha setting. (Just a theory from my side, I have not tested it.)

Do you know whether there is another way to make the rendered model semi-transparent above the background, for example by setting the default layer to semi-transparent?

Thanks,
Tibor