Basically, if you want the performance, buy it now. There might be a way to get slightly more juice to the standard motor, but when dealing with electric motors, software is no substitute for hardware.
Perhaps some day in the future, there will be shops that will replace your battery packs, inverters, motors, etc., and flash all the firmware needed to take advantage of them. But that's a ways off, IMHO.
You could always buy an S60 or S40 now (if the range will sufficed for your needs), and save your money for a newer Model S Performance in the future.