I had the same absurd Canon EU support argument thrown at me earlier this year when a Pro-1000 of mine had issues. Was also asked to make available a set of new inks and maintenance tanks up front for them to begin troubleshooting and fix the printer. I had several discussions about the unfairness of this, and insisted it could not be my problem what costs and materials they would need to troubleshoot and fix the unit under warranty.
I think they are way out of line trying to demand consumables for fixing warranty problems. They are reading those terms as the devil reads the bible, and seem very arrogant trying to solve the problem, not in any way expressing it might be an inconvenience that their product isn't working - almost making the customer the problem, not their own. Note that your warranty claim/issue is _not_ about the ink. You, as I did, do not have an issue with ink itself, and do not issue a warranty claim for the ink to be replaced. You have other printer issues. If they happen to require the use of ink for Canon to work out, that can hardly be the customers problem, but solely Canons. Does a car manufacturer require the car owner to pay for oils if the engine or gear train has obvious warranty issues, how about brake fluids if swapping brake calipers etc? It seems absurd, and I really hope you will argue the same, and help stop this nonsense. Is it really what they feel is "the right thing" to do? Canon, what do you benefit from this? Happy, loyal customers, good PR? I would think not.
Problems with their gear takes a lot of wasted time, money and energy for customers, so if anything, they could fairly compensate those troubles with actually supplying extra consumables instead.
I took a long and exhausting fight and they finally gave in and replaced the whole printer, not being able to defend their weak arguments and stand my counter arguments any longer. But it was a struggle that left bad marks in my thoughts about the company (heavily invested in their gear).
Best of luck with this. Sorry you have to go through it, and hope Canon will learn customer satisfaction is gold.