Well I solved the problem, the answer was pretty straightforward actually: obviosuly if you want to over expose by 1 stop (EV) the amount of light that will be recorded on a picture will be double. So to do this in MatLab you just have to double every pixel value. If the stops are 2, you have to quadruple the values, if it's just half a stop, then you have to multiply by 1.5 (50% more light in). Obviously pixels with a value will keep a value of and they'll be the clipped pixels.
This process doesn't take into account the camera response function but it's ok since the RAW file should have a linear response anyway.