I'm pretty sure that that is impossible with anchored objects.
Thanks. I'm laying out a book for print, but want also the ability to output it well to ePub (which I'm new to). An illustration takes up most of one page, and for the ePub I want it to follow the relevant paragraph. My understanding is that I need to anchor the illustration to that point in the text to get the ePub output right, but the end of the relevant paragraph falls on another spread!