a jam fcd would clamp the voltage at under standard starlet fuel cut (unless you adjust it internally) so you would gain nothing by doing that.
without knowing the exact scaling of the ecu, it is hard to tell, but as with anything, it can be done. you can run 2 bar on a standard ecu if you wanted too.
standard map sensor has a 2 bar range that is scaled between 0-5v, 0-2bar absolute or -1bar to +1bar relative to atmospheric pressure.
the sensor can read over or under that amount depending on where you live and the atmospheric pressure on the day. height above sea level and pressure changes in the weather affect this. you can often see as much as a 0.05bar swing day to day depending on weather systems.
anyway. if you get a map sensor with a larger range, but still with the normal 0-5v output that the ecu needs, then the voltage the ecu sees with be different for a given pressure. this will mess your map up. you can correct this with a rrpfr and a safc or similar. but it wont be ideal.
personally, if you want to run anything over 1.2 bar, i would get a piggyback that can take a wider ranged map sensor, or go stand alone.