zero shares = zero ownership, so I guess the S-Corp will have to pay tax on all it's income. 

I know this seems simplistic, but ...

If they have units use those.

Otherwise make it up.

For a small number of owners I will say there are 100 shares. 50% owners A & B each own 50.

Thanks sjrcpa.  That is pretty much what I decided to do.  I found an article by a cpa firm that said the same kind of thing but I always feel better with a second confirmation!