My Guy Cat Likes The Toilet Seat Up

Question
Hi Norman,
I am asking you this question because you answered someone's question about cats using human toilets.  This is a detailed problem with toilet training, so if you've never tried it I certainly won't fault you for not knowing the answer, but I figured you'd have a better guess than me!
I have a brother and sister, fixed, 4 year old pair.  They're both dominant with different things, but I think she's dominant at the litterbox.  When they were little I had problems with him using the floor, until I figured out she would hiss at him when "her" litterbox was dirty.  I got a second litterbox and they've been fine ever since.  
Now I'm trying to train them to use a toilet using "The Toilet Trained Cat" by Aston Lau- basically putting a plastic mixing bowl (which they like better than the suggested turkey pan) in the toilet, poking a little hole in it, and making the hole bigger until...
She won't usually "tell" me when she's using the toilet, but I'm pretty sure the accidents that happen are his (I catch him in the act sometimes-NO, I don't rub his face in it or anything barbaric like that).  He is more nervous about the process but will respond well to praise and treats and often lets me know when he needs to go.  
They were coming along slowly, but pretty well, with a softball-sized hole in the bowl when I had to leave town for a week.  I reverted to normal litter boxes when I was gone.  
When I came back, he didn't like the setup.  I had to close the hole with duct tape and lift the seat for him to use it.  I left it like that for a few days, then tried to put the seat down- and he started having accidents.  I even replaced my wooden seat with a padded seat, thinking he's like to dig his claws into that, and it didn't help.  They're still going in the bowl in the toilet, but I haven't even tried to poke a hole.  I don't think they're going to want to balance all 4 paws on the rim of a toilet with no seat, so I don't see the point.  They don't really seem to care about catnip, so I can't bribe them that way either.  Do you have any ideas of what I might try?
Thank you!

Answer
Charlotte,

I am afraid I have had no experience with training a cat to use a toilet.  I do know people who have done it and people who have had poor results.  You might check out the web for other methods people have used to train their cats to the toilet.  I have never heard of the mixing bowl idea as you have described, so I cannot comment.

In nature, cats use dirt or sand, so this is somewhat alien to their natural instincts.

I also have a friend who had to post a notice on her powder room wall that the toilet was shared with the cats, so they need to NOT lower the lid when they are done. When the notice was not followed the results were disastrous.

Good luck and best regards... Norm.