You REALLY arent getting this, peak power is no problem at all, at peak power the intake pressure is the same as atmospheric anyway essentially, so for full throttle you would be fine on the stock ECU.
The problem is everywhere other than full throttle.
If you are at 10% throttle for example, the stock ecu will be expecting to see a big vacuum at that throttle angle, but how are you going to show it a vacuum on a set of throttle bodies reliably?
You have to run a vacuum takeoff after the throttle plate, and then the problem that you get is that it will be very pulsey at low rpm, because induction stroke events are relatively infrequent, and its this pulsing that will cause the ECU to fuel wrongly and you CANT accurately map around it because the value you are trying to map will be pulsing up and down.
Some people try and smooth it by joining the 4 together, but the problem is then the 3 that arent at vacuum end up bleeding into the one that is. Its all just a massive lashup really.
You say you have a friend who maps, ask them if they have ever mapped a standard clio ECU, and if they have a complete definition file for one, if they say yes then you will be able to get it to just about work but it wont ever be great, and if they havent then you have no chance really.