It's been a while since I set up my robot. I wonder if maybe you could try to set up the DH parameters of the genserkins kinematic so that two joints coincide (ie. make one line of parameters zero).
Forward kinematics should be ok but I have no idea how the inverse kinematic will react.
You could install current master and modify the "melfa-sim" config.
I've tried to set up genserkins for a 5 DOF arm. Forward kinematics seems to work but the inverse kinematics totally fails.
So I'm afraid you would have to come up with your own kinematic. I'd try to figure out the math by using this (and yes you will need to make yourself familiar with matrices):
Making a length of zero is probably causing mathematical problems. But you could have a "dummy" joint at one end of the chain, and simply not drive it.
Scratch that idea, the inverse kins would want to use it in the solutions.
