I agree 110% with you on the subject of controller remapping, and this is something that should be in every 'next generation' games arsenal, period. There's no reason at all for these game developers to not put these options in games, what works for one group of narrow minded game testers isn't going to fly for a decent portion of the population that prefer and alternate controller layout, are disabled or just want a button on the controller to do what they want it to do instead of what their forced to have it do. I would love to see some next version of a big title game (ie Halo, CoD etc.) that came out without the Inverted option, just to see how many people gripe about not having that and can see what it's like too try and adjust to something that they have become accustomed too having.
I actually have no issues with most default controller layouts, though every now and then I just want a couple of buttons swapped around because of some idiots idea of a good layout versus what works best for me just doesn't cut it, but for the gamers that prefer an alternate layout (SouthPaw, Legacy etc.) or disabled gamers these 'default' controller layouts are completely unacceptable and it's almost down right sad what some gamers have to go thru to be able to enjoy the games they have paid for, or not even play them at all.
Sorry for the rant, back to the topic..
Making up the controller with a few jacks in it like that wouldn't be too difficult at all. The only issue you'd really run into is the loss of the button being Analog, being as all of them on the official PS3 controllers are. So for a racing game that would mean the gas pedal would be on or off, no in between at all, and even that issue could be worked around if need be by making up a different external button/pedal that was of the correct type to keep it Analog and getting a little more complex with the jack wiring in the controller, but it can be done.
I've done up a few controllers for disabled gamers as well as SP, LG etc. type layouts, and then some even more complex controllers, but this one here was the latest that has the L1/L2 buttons added to the right side of the controller. The right Rumble motor had to be removed to install those, and the left one was pulled as well by request since he had no need for them and was used to the older PS3 controllers that didn't have them anyway.
What you want done to an official PS3 controller is completely doable though, and if you need feel free to PM me about any of it as well.