Eric Meyer’s book “Eric Meyer on CSS” talks about this (Project 10) and the text wrap solutions that you found use the same principle.
Using a simple border-radius: 50% does not affect the shape of the content box, which are rectangular at this time. For example, see the demo by Kyle Sevenoaks.
There is a CSS3 module under development that addresses this issue:
http://dev.w3.org/csswg/css-shapes
However, this spec is still in draft mode and not currently supported, probably a year or two out.
The short answer is no, but hopefully the comments will provide some insight.