I have the same problem and stumbled on this attempt at an answer: techwhippet.com/play-hi8-tapes-without-camcorder/ Did you find a solution all those years ago? Mike.

In a Pixma MG3550 the main pads are in a trough just inside the right-side cover, as Nick says. The ink is pumped to the pads through the pipe, which has to be pulled off to remove the pads. Then two clips must be unclipped to remove the cover from the pads, which will bring some pads with it and leave some in the trough.

My printer is a Pixma MX715, so not the same. But is has a heavy scanner unit (with ADF) which has to be held up in order to replace ink tanks underneath. When you lift it up a lever swings down to act like a prop. So the lever is only attached at the pivot and you would not notice it was missing unless you wanted the scanner to be held up. Also the design is not the same as your photo. Worth checking?

I found this on https://forums.tomshardware.com and it worked for me on a Pixma mx715 BRIEFLY! 1. Turn OFF Power 2. Open the print head bay (as though you were about to change inks) 3. Turn ON power 4. Wait for print carriage to start moving to the left and let it go past half way 5. Before print carriage reaches left hand side (but after going halfway across) shut the cover. 6. Leave the Printer turned on 7. Good to go. (Very occasionally I have had to do this twice in a row to get past the error) Unfortunately before I was able to do anything useful the printer ceased to start up properly. A power monitor showed a brief consumption of 6W at plug-in, then it fell to zero and the power light did not light. (So I am in iFixIt to find a solution to that. The removable power supply has been cut open…)