No easy way but still a way I did was
to store 2 displayconfigs. In my
scenario I had a Nvidia card with two
monitors. I used the nview (or
something) utility that got activated
through after connecting the second
monitor. I created two profiles where
the main monitor was in one case the
right one and on the other the left
one. I had to restart photoshop
though to get the changes.
The other solution I remember was to
save two separate workspaces in photoshop having a normal and an inverted one.
I don't remember the details.. specially how useful this really got. After a time I recall making the effort to leave the workspaces as they were (ie ONE way only) and got around to using one monitor predominantly and the other as secondary.
this helped me to organize the windows more efficently since I lost less time searching on which monitor were which windows and also spend less time resizing and moving them around. In a way this sounds contradictory to having two monitors setup. For me it got easier. In the end that matters more than using the "full potential" of this setup.
(I'm now back to just one BIG monitor and miss a second one desperately)
I hope this helped you out