Multi-Monitor Mac -- Possible to keep one screen static in Mission Control?
Unfortunately I'm not aware of anything that can do what you're looking for. Mission Control is fairly limited in the ways in which you can customize it, either through the user interface or for developers. Similarly, OS X is pretty constrained in how you can configure multiple monitors (sadly, it's actually regressed a bit in this regard since 10.6).

You can set an app to appear in all spaces by right clicking its Dock icon, and selecting Assign To: All Desktops under the Options sub-menu. However this applies to all windows for that app, regardless of what monitor they're on. But if you keep all your iChat/Messages windows on your second display, it may be useful.