Well, you cannot change layouts per lists, but you could create 2 emulators the same, but have 1 filtered for horizontal, and 1 filtered for vertical games. This would enable you to use a layout for each orientation...
But I think Windows would have to be rotated to display MAMEWAH vertically...but you could try it out - if you card supports portrait resolutions, it may be able to switch to and from landscape/portrait?...