I don't think this can be done, not from what I see using the TinyMCE editor. Tried to insert a full image size attachment and position it right so text could wrap around it. Not an option I'm guessing?
I would love to see this in the core system.. But a plugin would be nice to.. Im kind of OCD and hate that i cant wrap text around images.. It just looks better and gives the forum a professional article feel.
Mainly spotted it because I uploaded a movie cover as an attachment, only about 100x30px in size. Wanted to float full size image top-right so text wrapped downwards around it. Just more for better presentation.
Doing it with CSS in an HTML webpage is dead easy.