4x10min @ FTP is going to be pretty tough no matter how you slice it. Think about it, FTP is your max power over the course of an hour (meaning riding until you feel like you'll die if you're doing it right), so 40 minutes of that isn't going to leave you in a much better place. I would shoot for 4x10 min at 95-100% ftp rather than right at it. The great thing about it, is once you start feeling like 4x10min @ FTP isn't killing you, it's time for another test... and then it kills you all over again.

So yea, it doesn't get any easier.