I'm not sure exactly what to suggest.... but I can tell you what I did.
I am up in the back corner of the 5th floor in a buiding in the city. I would probably be constantly going up and down if it weren't for the pads.

I bought two of the purina second nature litter boxes for dog......but instead of the litter i have the peepee pads down in them. [I also bought a diaper genie for the used ones.... and I flush his No. 2s immediately...]
I would put Riley in it, just as I would if he were to be going outside... after eating, after sleeping and after playing... and I would make a "HUUUUUUUUUGE" deal of it.... Clapping, telling him GOOOD BOY.... and just letting him know how Happy I was..... when he would go in it... I mean like if my neighbors heard me they probably thought i was crazy. I didn't really have any problems. After a few days.... I would just go over to it and call his name and point into it and tell him, Riley, Go Potty....
He will be 1-year old next month and I still do that every once in a while.
He is 100% peepee pad trained and he will also go outside....
When I take him to my parents house I can put a pad down in the corner and he will go use it when he needs to.
Good Luck!!