There is currently no ability to directly send low-level SPI messages from G-Code in Klipper today.
In the past, I have created this capability locally for debugging purposes - one can find that code at GitHub - KevinOConnor/klipper-dev at work-sensordebug-20231213 . Unfortunately, I doubt it would be useful for your uses as it seems you would need precise timing of the SPI messages (which the code on this development branch does not provide).
FYI, there have been discussions on inkjets in the past - for example: Inkjet Cartridge Integration .
-Kevin