Thing it probably depends what you wanted. You could do it illegally on a derelict site or on the side of a building, but that always runs the risk of being covered up. You could ask the owners of buildings around the Etihad if they were willing to have it up, that might be your best bet, but it'd probably take a fair bit of money to pay the artist and quite a bit of organizing. I really like street art, but even in cities with a better culture for it than Manchester, like in Berlin, Valencia, New York or Miami, the best pieces and work rarely last more than a year or two. I guess the nature of what it is makes it temporary.