I was trying to separate the different ink channel in gutenprint, I manage to create a driver for my 1400 wich use only the two light color channel, it's quite easy to realise. I still trying to figure out how to define this two channel to black color so I can print in greyscale on this two channel but I think it can be done.
I still waiting some part to mount my printer so I have time to figure it out, I think I can create a software to generate the second driver and configure it.
I ran into the same issue. On a 8 color printhead I could make changes to the XML files so depending on which setting I was using it would select only the left 4 or the right 4 nozzles to print. I never did figure out how to make multiple nozzles to be the same color.
If you figure that part out I could dig back in and help with setting the rest.