Looking for a tweak/app that will set permissions of a specific app to switch on 3g then when finished switch back to 2g?

basically i run my iphone 4s in 2g mode due to battery issues with 3g. but its annoying when i have to click 3g toggle then use reuqired app ie:safari,twitter,email etc? then i have to toggle 3g setting again to go back to 2g.??

Surely someone would be able to creat some some of hack/tweak to enable this to happen? is this possible?

any ideas or help would be appreciated.