After reading all of the posts to solve your problem and finding no real answer; makes me thinks my Little Memory Savor I made for just such problem as yuz guys has.
From Radio Shack, 1 9volt battery connector with lead wires ( one red and one black) aint that purty? 1 cigarette light plug.
Solder the leads keeping the polarity correct. Use shrink wrap for a real neat job.
With a nine volt battery in place and the gadget plugged into the light socket.
Disconnect the battery cable.
Turn the ignition switch to accessory position.
The gadget will hold all memories as original until the battery is exhausted or you return to normal condition.
I've had my Donald's El Cheapo for many many years and haven't had a memory loss yet.
Happy Trails Beep Beep from Houston!!!
Donald, El Cheapo