ASP.Net 2.0 Menu Control SeparatorImageUrl

[GroupReader]

I can set the SeparatorImageU rl at runtime to display a separator
image between menu items - all works fine there.

How can I have the image "stretch" or "repeat" to fill up the width of
my Menu Item?

I know I could just make the separator image longer, but then all my
menus will be longer too. That's not what I want.

Thanks.