Does anyone have any experience writing (health) plan documents for PEO's? Any advice regarding regulatory issues or special plan wording for these entities would be a help.

I suggest that you first go to the Q&A columns and visit:

Who's the Employer?
Advanced Plan Design?
401k
Cafeteria Plans

I might not have got the names of the Q&A columns right but you should easily find the ones related to the above 4.

Second, find out what the larger PEOs have. They have spent a lot of resources and have had a lot of litigation that has caused them to provide their benefits in the manner that they do.

Third, find out what the State Dept of Insurance in each state that your client will operate in has to say about PEOs offering benefits. You might be surprised at the restrictions. Look up NJ Small Employer Health Benefits Program Advisory Bulletin 00-SEH-02 issued July 28, 2000, this will give you a guide for those states that have similar restrictions hidden in their small group regulations. Also search MEWA regulations.