How can I fix the Dual Monitor Fullscreen issue without updating to Maverick
This was fixed in Mavericks as you are aware, but I don't know of any canonical way to fix this for apps in prior versions of OS X, and even app specific fixes don't work properly.

Whilst you said without updating to Mavericks, this really would be the best option since it is the 'official' fix to a core part of OS X.