Hi NikosGuitar,

Practically, I would recommend fingerpicking as close the bridge as possible.  Signal-Processing-wise, I would recommend using the Ominpressor with ratio of around 3, release around 0.1 – 0.2 Secs and attack probably greater than 0.01 Secs.  You should also move the Contour all the way left for a Feed-foward compressor. and you'll probably want to brighten up the sound by boosting the High EQ knob.  You'll have to set the Threshold based on your guitar and use the Output Gain in Space for make up gain (or some external boost pedal post Space).  

The idea with this being you want the compressor to only act after the initial attack, bringing down the gain of the note release and decay, but keeping the attack louder.   The make-up gain will then bring the whole signal back up.