Extending printers.conf with own attributes

Hi,

Can anyone tell me which files are involved in saving/reading an attribute 
from/to printers.conf?
I'd like to extend the add/modify printer dialog with some attributes we would 
need to be saved with each printer. So I found out that
scheduler/ipp.c, scheduler/printers.c, cgi-bin/admin.c ... and some more are 
all involved in editing printers.conf.
I also extended it as far as my attribute keys are saved into printers.conf, 
but not the value. Also if I've entered a value manually into printers.conf the 
templates (especially modify-printer.tmpl) are not filled out with the values.
Can anybody give me a hint or howto extend printers.conf?

Or would it be possible to implement a generic solution for attributes in 
printers.conf: Let's say every attribute key which starts like "X_" (e.g. 
X_newkey) would be read/saved by cups and the value of this could be used in 
templates.
What do you think about it?

Best regards,
Johannes