Bob,
You don't usually do this, but today you have just come up with a complete bucket of poo. Sorry, buddy, but that is just so wrong in almost every respect.
I hardly know where to start.
Firstly, the squadrons don't have twice as many pilots as they need. You work the rest out regarding that one. Next, no pilot can just jump in the back seat, where many have never even been before, and automatically work all the kit - let alone become practiced and proficient to the degree where they could be declared operational.
QFIs, QWI pilots, IREs, etc, fly in the back seat. Experienced people with additional back seat training. So, you going to take a junior pilot, still working up or at very least getting good at what we need him to do and now tell him he's got to get proficient in tha back seat too? Remember that all the time he's in the back seat, he's not available to fly in his own seat, therefore his progression slows by 50%. They will not get more airborne time, it's just that half of it will be in the wrong place.
And as for this...
Once the guy learns the switches surely he could cope. He may not immediately do the job in the same way as a WSO but he wouldn't be terrible.
He wouldn't be terrible? This is the measure of the RAF's operational aircrew you are suggesting?
You see how rediculous your post is or would further explanation help?