How to make slurs ignore stems?

[Jakub Pavlík]

In regular modern scores it is logical that the ends of a slur attach to a 
notehead or to an end of a stem, depending on the direction of stems of the 
notes connected by the slur.

I'm typesetting chant transcriptions and make stems transparent:
\override Stem #'transparent = ##t
Some slurs, attached to invisible stems, then "fly high over the notes".

Is there any way to tell LilyPond to ignore stems when making slurs and attach 
slur always to noteheads?

(I attach an image showing the problem. Red dots emphasize slurs attached to 
invisible stems.)

Thanks for any help.
Jakub

slursexamples.png
Description: PNG image