The Dark Side
There are a number of dark side options. All of these will mean, at least, that you don't get blamed for the project being late. However, they are irrational in the sense that they won't solve the problem.
Dark Side 1: Don't Tell Anyone
This sounds silly but it can be very effective. Faced with the fact that you will be at least six weeks late, you and your team hunker down. You continue to report to your sponsor and stakeholders that everything is fine and begin to drop little hints that there are some small problems that you and the team are currently working on correcting. With luck, this will buy you enough time to put some of the other Dark Side strategies into action. With a lot of luck, one of your team members may leave ...