I found how to switch the modes through code and I found out two interesting facts with phonegap
1) Retina mode on iPhone actually improves performance by around 5fps in my game!
2) Retina mode on iPad kills performance on an ipad3 with retina on 1fps retina off 20-30fps!!!!!
Which brings me to ask, is there any way to programmatically switch off retina based on the device we are using?