Replacing Light inks with gray on Canon MP970

Since printing with OEM ink is getting too expensive, I'm switching to third-party ink. But finding a high-quality ink is rather difficult around since my printer, a Canon MP970, has 1pl minimum droplet size and I'm printing rarely, so I have to use good formulated ink with decent micro filtration in order to avoid clogging and printing head damage. I've found good source of inks locally but for MP980/MG8150. The seller does not offer Photo Magenta nor Photo Cyan for my printer (CLI-8 ChromaLife inks), but has Gray ink instead for next generation printers (521 ChromaLife+).

I've been thinking if it is possible to run my MP970 like a MP980/MP990 with gray ink instead of PC/PM inks, which will probably involve using a custom RIP software.

Has anyone any experience or view if my idea is possible at all?