i wondered about a slight wax product ? When i used to tow a RIB years ago as a diver we used to spray the disks with WD40 after a dip in the sea used to burn off in a few hundread yards.IMO no! Anything to spray to mitigate such surface rust film will also be a lubricant......and you don't want (petroleum based) lubricants on your brakes disks
I know guys who do use it, I've not needed it myself as yet, I use their cleaning products, I can't fault any of their stuff I've used, but I've no first hand experience of this one, sorry.Do you use it yourself, Gav? Could be handy on a couple of the bikes that see very little use over the cooler season!
You'll need to get the car up so you can get at the insides of the discs and rotate the wheels to get at the bits hidden by the callipers. If you have vented discs, you'll need the wheels off to get at the middle too.
No point in doing it half heartedly. You'll end up with uneven disc wear, requiring replacements earlier than you would leaving them untreated.
So just leave them untreated! The surface rust (if left even) will rub off after a rotation when the brakes are first applied and will barely affect the longevity of the discs and pads. If you can park on the flat, leave the handbrake off and the car in gear/P to keep the rust even.