Mix of bgiframe and opacity in IE

Hey devs,
has anyone ever tried to apply opacity to an overlay element, eg. via
css("opacity", "0.5") while the bgiframe-plugin is applied to that
element?
The effect I'm getting: A white overlay, nothing else.
If anyone has a solution for this, please share it. Otherwise I'll
just exclude the opacity in IE, maybe depending on bgiframe plugin
being present.
Thanks
Jörn