I'm sure that card windows in Webdirect will see the light of day in the next 2-3 releases. The option today is to use popovers or fake a card window. I think the latter will make upgrading to them later a lot easier since it wouldn't touch your layouts.
I'm using a rectangle to place all my objects on. Then I select a blackish background on a body part only form. Transparency won't work .
Once I have all my objects placed I group them together with the rectangle and center it on the page. From there, uncheck all of the anchors so the page stays centered when resized.
Make the card smaller or equal to its parent screen so you don't get the scroll bars in your browser. In the new window script option step I uncheck everything except Resize.
Anyone have any additional tips or ways? Would love to hear.