I use a non-circumvention agreement that my lawyer drew up for me. It basically says that the investor can't buy the property any other way than through you for 5 years.
If it were me, I would not use the investors contract. Think about it, wouldn't his contract be beneficial for "him" to use? If you want to protect yourself, you should have your own contract drawn up. The lawyer shouldn't cost too much, and it will definitely be worth it so you don't get ripped off by the investor.
Once you've paid the lawyer once, you'll be able to use the agreement on future deals.
This is my opinion, but feel free to do what you want. I personally would like to see you protected, just in case

Jeff