The one business that did something sorta like what individuals are trying to copy is ASICMINER? where they took investors money and gave them shares in the business.
This rental things you have described will not work with people who can understand basic math and the risk involved in trusting you to maintain the equipment and 24/7 mining uptime.
Your original post reads: "Anyone interested in giving me money up front to go buy the computer equipment needed and then pay me x dollars to give you (x dollars + y%) back every month." Makes no sense... you have to make money at this and the way you do it is y% is less than what is actually getting mined.
For you: You have no money to buy the equipment yourself. So people asking why don't you just mine yourself... good question... and that is the answer.
For customers: After you pay for about 2-4 months rental you will have paid the entire cost of the equipment that you could have bought yourself and mined.
So how do this work for anyone???
I will definitely look into doing something like ASICMINER. I was trying to offer a service for users who don't want to pay electricity or want to get more profit because they don't have to build an entire rig dedicated to mining.