Digital BW, The Print

Sorry to be running off at the keyboard here but I just had another idea that might be very simple for you, and I've had too 
much coffee. You may be able to leave everything the same, but find a media setting in the driver that puts down less ink. 
Do some small tests of the problem values (they'll shift a bit so include the general tonal area) on different media settings. 
If one works, it'll print too light, but you should be able to come up with an adjustment to the file that will allow you to use 
the same sep curves. You may loose some max K, but it might be minimal.
Some media settings change some of the other inks more than the K, to a suprising degree with some drivers, and that's 
what you need.
Tyler