Hm, I'm not really sure what you're asking for...
With this build of litestep:
http://www.technoirotica.com/~rabidcow/litestep/litestep-mm-030211.zip
You can name your monitors:
MonitorNames one two
and it will provide you with variables for the size and position of each of them:
$oneResolutionX$
$twoTop$
If you provide sensible defaults, this will let you create a theme that will work on single monitor systems with a normal build, and multimonitor systems with this build. (so you don't have to include a whole build of ls like the olden days)
for example:
oneResolutionX $ResolutionX$
oneResolutionY $ResolutionY$
oneLeft 0
oneTop 0
oneRight $oneLeft+oneResolutionX$
oneBottom $oneTop+oneResolutionX$
etc.
The hard part is figuring what sets of edges and positions you need to add together to get each module in the right place. (I've mostly given up on that myself, but it should be possible.) I think most of these differences only show up when you have monitors in negative space tho. (and there's enough other problems that you probably should ignore negative space monitors for the sake of your sanity, they really need native support in the modules.)
That is, with on top:
ModuleX $oneLeft+50$
with on bottom:
ModuleX $allLeft-oneLeft+50$
or maybe:
ModuleX $oneLeft-allLeft+50$
or maybe something else, it would require actual thought to figure out which is correct, and experimentation to figure out which the module actually needs after it does funky corrections.
There's some other tricks in this build, like creating fake additional monitors, but that's not really important. (actually, that might be everything, I'd have to go look)