The problem with getting the center nut lose from what we used to call the clutch boss is that the boss itself will turn, the clutch tool is a tool that is made to hold the boss so you can get its bolt lose.
You might be able to us an oil filter wrench, or a strap wrench. I never bought a clutch tool, but I have made them.
The last one I made I used one of the old metal clutch plates and welded a piece of metal to the face and edge of it for a handle. The metal clutch plate is splined to fit the teeth of the inner boss.
MarkC