You would need to prepare the 1120-S S-Corp tax return in order to produce a K-1.  

If youre not experienced in SCorps, I would strongly suggest he find someone that is, they are a whole different ballgame from preparing a 1040.

S-Corp returns were due back on March 15th so unless someone filed an extension for it, hes already over a month late.

Personally, Id tell this joker to go kick rocks, waiting till this late of a date and then shoving the Corp filing off on you, sounds like hes going to be more headaches than hes worth.