I don't think there is a way to do this. When you are referring to the separator bar, I am thinking you are meaning that at the end of a line where you input a URL into a menu, the very last option you can set to 1 and that will put a bar inbetween the menus. That bar isn't the character "|", its actually part of the border of the layer that the menu item exists in. That tag just turns it on.
But here is a nice little workaround for you.
In your menu style, make sure the padding for the items is zero. Then in the text for each menu item that is displayed put ":" on either side and it will look the way you want.
i.e.
":: Item 1 :","show-menu=first","#",......,0
": Item 2 :","show-menu=second","#",.....,0
": Item 3 :","show-menu=third","#",.....,0
": Item 4 ::","show-menu=fourth","#",.....,0
This will produce the following if your menu padding is 0....:
:: Item 1 :: Item 2 :: Item 3 :: Item 4 ::
Give it a shot!
