again: as fast as possible

[Stefan Thomas]

Dear Lilypondusers,
I've read the mail concerning the slashed beams under
http://lists.gnu.org/archive/html/lilypond-user/2006-12/msg00253.html.
But there is one thing, that isn't convincing for me:
in my opinion the slash is too short.
Is there a possibility to make it longer?
For myself I made experiments with postscript. I made a macro for the slash:

slash = \markup {
   \postscript #"0.1 setlinewidth
                -0.3 1 moveto
                 2.5 4.5 lineto
                 stroke" }
But now the starting position and the length are not always, what I need.
Is it possible to write a macro for the "moveto" and the "lineto" in the 
markup command?
I'm thinking of something like
slashposition = {position of "moveto" position of "lineto"}
Thanks for any advice!
Stefan