GM pays the dealer a certain amount for labor to install them, maybe 2 hours (that's what my salesman thought it was). My dealer said I can have whoever I want install the stripes and the dealer will pay them what GM would have paid for the dealer to install. If it costs over that, you may need to make up the difference.
If they are not willing to contribute that to getting them installed, then I'd make them do it. With the dealer installing them, if you are not satisfied with the final product, I would think you could complain and they would have to do them over. (they will come up without ruining the paint...so I've heard)
I think I'll be taking mine to a body show that I do the computer work for, they assured me he does amazing work.