How do I export a keynote slide to pdf with a transparent background?

I use Keynote for creating figures for a report I'm currently writing and layouting in Adobe InDesign.

Unfortunately I have run in to a quite annoying problem.

Because of the page-layout and background graphics in my main report, I need to be able to export the figures without the white background which comes as standard. I tried to remove the background in "Master & layout" (my Keynote is in Danish, not sure if it's called the same in English), which is suggested to bring background transparency when exporting to Quicktime movies. I doesn't seem to have any effect when exporting to pdf though.

When importing the pdf's into InDesign the figures comes up with a white background instead of the wanted transparent.

My choice of pdf over png is because of the vector graphics.

Is it possible to export to pdf's with a transparent background?