Hi Grendel - it's possible but it's not particularly high on the radar since circular selection hasn't really been mentioned very often as far as I remember.

If it's an important feature for you, put it on the Top 5 feature request list for v3 thread here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=3628.1

Would you expect it to select things only entirely inside the circle or anything that touches the circle? Or would it be for selecting control points only?

- Michael