Yes, you can. There are people that have. You don't need a product like that, just slowly raise the litter box to the toilet, then put it on the toilet, then find a bowl that fits in a toilet and slowly replace litter in it and then when it's empty replace the littler with more and more water, then to remove the bowl entirely.
I however can not recommend it in the slightest. Cats are not meant to use the toilet, it isn't natural to them and in many cases the cat will start using other locations to pee and poop, most often bathtubs and sinks. If they fall in the toilet they may spook from using it too and start going other places because of that. Or if a cat gets old and arthritic, jumping up and positioning on a toilet seems really unfair.
On the off chance that a cat may start peeing around the house, I would never do this. A cat peeing around the house is a nightmare. Moreover, I've read that cats that go in the toilet do not recognize other toilets as a place to go, if you move house or need to leave the cat somewhere else or the cat can't get in the bathroom when it needs to... trouble!
I personally would never toliet train a cat. Its unsanitary to have to use the same toliet as them. What if they develope diareah and get it everywhere. Mine are getting over giardia right now (city water has caused animals and residents to get it sence boil order was not put out). I wouldnt want to chance that.