i used piece of copper pipe (the size that go's into household rads etc).
fits perfect in flywheel. just wiggle centreplate a bit (just nip nuts on cover so plate is pinched but moves) 'till it's in the middle.
done mine this way and it was perfect! box slipped on a treat i tell the!
I don't actually have a clutch tool either. I use a long 12mm bolt and a roll of 2 inch masking tape to make my clutch tool the right size for each application. For a first timer its one less variable to deal with if the clutch is guaranteed centred.
Cheers
D