leftseparator
rightseparator
leftseparatoractive
rightseparatoractive
(and the reason i'm not using solpart):
leftseparatorselected(mouseover)
rightseparatorselected(mouseover)

Is there any css or xml tweaks that can mimic the solpart separators for these 3 states?

If all you want is a simple line seperator just use left and right borders. If you want to get a bit more complex you can use images for the list items that have any seperator you want. Basically you follow the "sliding" door method to create the seperator you want. I tend though to just use a background image per list item and set it to align to the left side. Then pad a:link a bit to ensure the text for the link is not over the image.  Its pretty basic but works. One thing I keep finding out about housemenu is the simpler the solution the more impressive you can make your menus look. lol