Most (all) major ISP's do have DC"s that you can colo in (including comast). Just call up their business services line and ask.

So, yes, you can colo in one of your ISP's DC's. Netflix is doing just that (which is why it's not a peering agreement, it's a colo agreement). They just don't get charged because they are saving the ISP the money they would normally charge for the colo service (sometimes more).