Controlling 4 dc motor using arduino duemilanov

i am a new bee here...
I want to connect 4 dc motors (12v) to the arduino to make a normal bot which can run forward,backward and can also turn left and right (by running motors of both sides in opposite direction) .A simple solution would be to use a quad motor shield for the same.But i am from india and there isn't 1 available here.The only motor shield which i can use is this

But it states that it can only handle 2 dc motors .From what i get i think that it cannot control 4 dc motors separately but i can use them if i pair 2 motors from each side to get a single terminal. i need 4 dc motors so that my bot can effectively turn left and right .
What i think is that pairing 2 dc motors from each side and taking out a single terminal from both and then connecting it to this shield.

Is this possible???
If not then plz suggest me some solution..

It might be possible to use two of those shields if one was adapted to connect the four different pins (9 and 10 instead of 3 and 11 for the PWM, perhaps 7,8 for the direction pins. This would take some bodging of the board (cutting tracks and soldering thin wires between the relevant pins and traces - not a beginner's task really.

Alternatively instead of stacking them with headers, stack them by soldering wires from one to the other as necessary (one has header pins still to plug into Arduino)...

Then rewrite the library to match?