Using Roth IRA funds as down payment, not full deal

[Justin P.]

Hello, I've lurked on quite a few of these posts and have found several answers, but I have a couple more questions. I know if I use a Roth IRA to purchase a property, all expenses have to come from the Roth and all proceeds have to go back into the Roth in order to take advantage of tax-free growth. If I combine funds from my Roth with others to make a down payment, can I still get some tax benefits? Let me make an example:

Buy a property $100,000 all in. Use $20,000 from Roth, $20,000 cash, finance $60,000.  If I flip it for $140,000, can 20% ($8k) of the $40,000 gains be put back into the Roth, 50% since it was half Roth half cash that I put in to it, or is there another scenario I'm not thinking of? 

Thank you in advance for your help!