I was hoping to do something like this in OOo this summer, and couldn’t. So I filed a bug. Looks like that paid off. (I also got this one fixed earlier in the summer.) Big thanks to Jan and Caolan- it might not seem like much, but making it easier for people to make beautiful presentations is one solid step towards making people actually like OOo.
Now, if only there were s5 export :) (I love s5 as a machine-independent presentation format, but actually writing a good-looking presentation in it requires CSS I don’t have.)