Allowed to contribute some commission as downpayment?

I am currently trying to work out a deal with one of my clients.  The home they want to buy is from a builder offering a 14% realtor/buyer co-op.  I have heard that it is illegal for a builder to contribute their incentive as downpayment for a buyer.  But I just would like to know if it's legal to contribute some of my net commission as downpayment for my client?  I was planning to take the whole 14% for the commission, contribute 5% to my buyer, and just take the rest as my commission.  Is this possible?  If not, then is there another way to get around to helping contribute some downpayment to my client?  I am new to this so please bare with me.  Any help would greatly be appreciated.