I think you can do it. It would be vital that you establish a different qualified retirement account that is not included in the original SEPP. Check out this website for good info and then back it by reading referenced IRS docs Welcome to 72t on the Net
Edit - I have zero knowledge of 401(k)s, but I think you can make penalty free withdrawals if you leave your employer after you turn 55. Somebody will come along and correct me if I am wrong, but if that is the case I don't guess you would want to burden yourself with the potential complications of dealing with a SEPP. But you mentioned both IRAs and 401(k), are you planning on doing your SEPP from both?