In order to create one yourself you will need two shapes (separate objects) and some unflowed text. Select all three and do Text->Flow into frame. The order in which the frames are used depends on the order in which you selected them, so if it's wrong hit undo and try again.
Well, I wouldn't call this UI perfect, especially because the text flows first into the frame, you select last, but it's great to know that his works. What I would ask for is a little plus at the bottom right of the frame, if it's full and the option to connect it to any other object... just like in Scribus and InDesign :)
The hole in the middle of flowsample.svg is done with a flowRegionExclude tag, but there's no need for that (and, in fact, no UI for it either) - you can just create a compound shape using, for example, Path->Difference.
Well, true, but you know, the flowREgionExclude is a lot sexier, when you think of text wrapping around other objects. I have filed an RFE about that quite some time ago :)
Thanks for the hints!
David