I've posted a patch on sourceforge that extends tick
labels to allow for a dash of user-specified length
to come between the text label and the actual tick.
I'm attaching an example plot below. (The script
to generate this example is on sourceforge).
The alignment of the dash with the text is less
than ideal in the PNG output, but it appears that
the font-metrics are backend dependent - the
quality of the alignment seems to differ based
on the selected backend.
Please let me know if there are any modifications
to the patch which would make it a better candidate
for incorporation into the mainline source.