Bullcrap and I say again, Total Bullcrap.
Yes. Romney could very well pick off a Utah or Idaho, maybe even NH, but he would damage the republican ticket. Hilary would coast as Romney would win no other states, while sinking Trump.
If this scenario were possible, it would cause a revolution. A guy who only wins one state (Utah) would not be President long. Likely, he wouldn’t even get to swear his oath of office. Mass riots would seize Washington DC.
Wanna see how pissed off the trump public will be if Romney helps hillary to the presidency?