Does anyone know if theres an app to disable the TV Out on the iphone 3gs with the AV cable connected to charge?

Im asking because i use the apple AV cable connected to my proclip to my rear entertainment system and i cant see any videos on the iphone display with the cable plugged in. I'd rather not have multiple cables to switch around for watching in the front or back of the vehicle. I tried searching for jailbroken apps but couldnt come up with anything. Seems ridiculous that apple wouldn't add that setting.