You won't harm the ecu by adding a few more diodes, add two and then study the response, and this will make the dead spot a little more, and the response will be slower, then try even 3 diodes or even 4 , but all diodes must face the same way (like batteries in a torch)
Also is there any way you can note the RPM v/s the pedal travel on some sort of cardboard scale held steadily next to the pedal, this a little more scietific way to find out what changes have occured to the response for the same amount of pedal travel, the reves should in my opinion rev slower.
Bear in mind that by adding more diodes the upper most voltage on the wiper pins will be lower than before and so under load the car engi8ne will not reach full revs, but this is to be expected with this method. This should not be an issue with learner drivers.
