Actually, you have to do it without the leash of learning, or it tells him he's good for being curious and he drops the food. Using the leash of aggression will sometimes better, but it is best to rub his tummy with no leash attached.
Also, I'm not sure what it is, but something in my recent style of play has been causing me to continually win on the first try on the final battle, even with a creature I just got at the beginning of the run. The last one was a leopard on speedrun (yes, I know I abuse the incredibleness of the leopard :laugh2 ) and I didn't even have to heal. I just guided him to guard for most of the time and strike the moment a weakness presented itself; I didn't have it use any miracles, as I'd taught it none except water on accident in Land 4, this being a speedrun, and I didn't use special attacks until the very end when Nemesis had used up his heals, and I still had half-health (come to think of it, it was about 80% fat because I had never taught it to pace its eating, either; Not sure about strength, but I imagine it was low), and then I just spammed the pentagram until Nemesis's creature was defeated.
So, maybe try a similar setup.
My typical casual "speedrun" (contradiction of terms, I know) lasts about four hours, so these are brand-new creatures that have been doing this. The next time I pla through, Imma try to use the gorilla, so I will see if the strategy works with other creatures.