There's a lot of threads about racks you should read thru, to give you ideas on how to fix the problem, and about how rack weight ratings don't mean much (such as, if you're riding on a completely flat road totally straight without wiggling it via pedalling/etc., then probably most of the racks can hold what they say they can, but when you hit a bump, you multiply the weight that's on the rack by the forces involved, which are not all vertical depending on the angle you hit the bump at, then you get into pedalling wiggle to fatigue the rack, etc.).
That said, you could build a rack that is supported not from the seatpost itself, but from the frame, that uses the suspension both for Cecil's comfort and to minimize stresses on the rack itself.
It'd use 1" square 1/16" (maybe 1/32") wall steel tubes on either side of the main frame, that run from the downtube/toptube intersection at the headtube both in front of and behind it, back across the top of the short curved tube at the point just in front of the seatpost, back to the rear of Cecil's box.
(EDIT: the start point above probably won't work and leave room for suspension movement, but maybe from just below the downtube would, clamped to the downtube and the headtube itself just above the crown race--see attached pic for one possible idea with straigth tubes, curved tubes would give you more swingarm clearance, etc)
These would cross connect to each other at those two (three) points, (preferably welded to each other, as the frame is probably aluminum and you wouldn't want to weld to it. If you have to you could bolt them together, but you'll need to use tubes inside the bolt holes inside each tube and between each tube as spacers so the walls don't crush).
U-bolts can then be used to clamp the rack to the frame itself, with metal plates shaped to fit the curves of the frame tubing between the U-bolts and the frame tubes to spread the load over as much surface area as practical.
Then a pair of tubes would run diagonally forward and down from the rear tips of the tubes above to the BB area of the frame, and be U-bolted to that (or the seattube above it, if the middrive makes it impractical to directly connect to the BB shell). Because of the swingarm, you'd probably have to gently curve these tubes outward and then back inward, so they clear the swingarm in it's full travel up and down.
If you don't use any rear triangulation to the BB area, it'll be a lot less sturdy and need thicker wall tubing to do the same job.
Then you could remove the rack's insufficient swingarm-mounted supports, and clamp or bolt the rack to these twin tubes instead.
Then you could probably carry Cecil, cargo, *and* a human on the rack without breaking it.
You could probably get away with thinner wall tubing, but I've tended to go for certainty and heavier rather than chancing anything.