I'm sure there would be a way Faye, no reason that it couldn't be worked out. I am just in the process of adding a second floor to Maximus von Lichtenwalder's secure cage. So that when he is not out on the bed (I have a waterproof picnic blanket I put on to protect the douvet, plastic side up then cover that with quilted coverlets for him to be on top of) he can have better exercise area. He loves the bed so much for the space it gives him, but when I am not home to supervise the cat then he goes to the secure cage.
I think I've altered his cage every week since he came to me a month ago! I use temporary materials and see how they work out in practice, then I list what he really seems to like the most and adjust platforms and so on...
He also seems to really enjoy the novelty of the new changes...lol
I think they are hardwired to pee on grass and hay, like they were intended to fertilise the world. I often change the hay and shavings underneath it, as soon as I feel its wet. Maximus von Lichtenwalder tends to go pee in only two place in his cage so it's easy for me. But he poops on his running tracks, where he sleeps and in his hay. He avoids pooping in his pellets or on his veggies mat.