this would be your basic circuit, with all of your VIN lines tied together and fed 0-4V (0-4Amp per mosfet) and all of your VOUT lines tied together fed into an op amp in a summing configuration,
http://upload.wikimedia.org/wikipedia/commons/thumb/3/3e/Op-Amp_Summing_Amplifier.svg/200px-Op-Amp_Summing_Amplifier.svg.pngwhere rf = 10K aswell,
The power traces are 2mm wide on both layers, and signal wires are 20 mil (yes i am mixing units,)
this would be for a 5cm x 5cm PCB, the 5V would be the supply to the op amp, with ground being common to the mosfets, all nice and pretty,
D1 is drain 1 on a mosfet, G1 is the gate, and ground goes to your ground bus bar, the large holes are 1.5mm with a 3.3mm pad feel free to change as required,
the smaller holes are 1mm with a 2mm pad, for the gates and lower corner inputs, (i consolidated after making the images)
there is still the 4th op amp to use, and with some shifting someone could easily break out some pins for whatever they wish, this is just the nicest design that came to mind for 5x5cm
red is copper side, and green is component side, though its not that critical, as worst case it just involves flipping the op amp 180 degrees,
hope this helps, the last post just covered some of the bacground theory, with 4V in, means 0.4V on the + input of the op amp, and being how op amps love keeping there 2 inputs at the same voltage, it will then regulate the mosfet until it passes enough current to produce 0.4V across the sense resistor, (mosfets linear range from datasheet for 0-4A is ~1.8 to 3.2V)
while most of this is to help you i am dumping in bits of info so any luckers or later readers can actually understand how it works
edit: R6 and C1 and there repeated ones are just some optional footprints to try and stabalise the circuit a little if your mosfet is oscillating, though i may have got it wrong and i may need to be added between the inverting and non inverting instead, also
the pin numbers on the schematic are meaningless, they where just from me throwing together a quick diagram, though the indicator mark on the pcb is correct,