circle around noteheads?

[lfanele]

hello lilypond-users,
is there a way to draw a circle around a note-head?
so far i tried it:
- with balloon help, but I didn't like the looks of it (btw: is there  
a way to set the size of the balloon?)
- manually with \markup{ \circle " "} and extra-offset, which is  
quite time-consuming

any better ideas? as always thanks a lot!
stephen