commissions reimbursements

[Ryan J.]

I am negotiating a deal with the sellers agent to have him represent me (buyer) to purchase a home.  Normally I'd hire my own agent, but due to the craziness of the market I need an inside edge.  The commissions split is 4% of which 2.5% goes to the buyers agent and 1.5% to the sellers agent.  My deal is give him 1% of the buyers commission while I get to keep the remaining (1.5%).  

My question is how do we structure this into the purchase and sale agreement? His brokerage sent the attached doc (form 40).  But I've never seen a form like this before... Is it legit?