Function to override the stem direction and flag of a single note?

[Andy Chase]

Hello all,

Let me establish a bit of context before getting to the meat of my question: I 
mainly use LilyPond for transcribing 5-string banjo music from the 19th and 
early 20th centuries.  Pretty much all of this music is in standard notation, 
but there’s one very banjo-specific convention that I haven’t been able to 
figure out how to replicate using LilyPond.

On 5-string banjo, the 5th string is a short drone starting at the 5th fret 
position; it’s typically always played open with the thumb.  On modern banjos 
in standard tuning, the note is G4.  Because there are several ways to play a 
G4 across the banjo fingerboard, there was a convention used for 5th string 
notes:  They were always set with the stem up, and with a sixteenth note flag 
(regardless of the actual note duration.) 

Here is an example from a piece published in 1882 (In this instance the 5th 
string is actually an E4, as banjos used to be tuned lower.  The clef is 
treble_8.): http://andychase.net/img/banjo_5th_string_notation.png

All of which is to explain why I’m asking whether it is possible to write a 
function to format notes in this way, that is:

1) Stem always pointing up  2) Always using a 16th note flag (regardless of the 
note’s actual duration)

I’ve spent a fair amount of time tinkering with this but I’m a little bit out 
of my depth.  

Thanks for any suggestions!

-Andy