Using circles in \tabFullNotation

[Kuredant]

Hello,

I'm trying to have an output similar to the attached images when using 
\tabFullNotation: half-notes and chords circled with a single stem and 
whole notes and chords circled with no stem.

Reading the source code for \tabFullNotation, I think I need to 
\override TabStaff.Stem.stencil with a custom Scheme function, but I'm 
note sure how to do that. Can someone point me in the right direction?

half-whole-notes.jpg
Description: JPEG image

chords.jpg
Description: JPEG image