That plan won't work well. Along with the new headtube, you will also need to buy headlugs to fit the 36mm headtube. By then you will have spent quite a bit more than what you saved on the special.
I can think of two options here. First, stick with the tube and lug special and also order the fork kit with the 1 inch steerer (farther down on the specials page). Make sure you know the proper length steerer if you go threaded. If unthreaded, make sure you can find a 1 inch unthreaded headset too. I think they are out there, haven't ever looked for one.
The other option is to start over and decide if you want oversize or double oversize and choose compatable tubes and lugs that aren't on special. Make sure you specify the headtube size when ordering both the lugs and the tubes if you decide to go oversize.
Long post but I hope it helps. Good luck.