QTR-Quadtone RIP

I would like to re-commission a 220 printer that I have to use MIS
UTR2 inks in a CIS but be able to use either the MK or PK inks by
creating the appropriate curve in QTR.(ie. making the  PK "not used"
when printing a matte print or vice versa for glossy printing) The
hitch is that the UTR2 ink set is an ink set with either a PK or an MK
black and 5 other degrees of black (grey). In my scheme one of the 5
grey inks would have to be replaced by the additional black ink. The
question is one: is this practicable and two: which of the 5 grey inks
can be sacrificed?

Any thoughts?

Thanks for your time