Have you talked to him about his relatives that may be able to gift him the rest of the downpayment?

(Through a lender) Minimum down payment is 20%, no gifts allowed for help, closing costs are also out of pocket.

As in the hypothetical Steve Babiak has mentioned, the city here requires any private street be brought up to city standards before they take the "gift".

He's got the gift.

She stopped by that very night with a card and a gift of candied almonds.

If they plan on taking a capital gains tax hit on selling the property, you can point out the advantages of an installment sale & getting a return much higher that the bank or bond market can provide them ( they can also help their new graduate daughter by gifting her the income now or in the future if they wish.)Your exit strategy can make this a bit more complicated.  

Since starting in real estate, I've had three loans or gifts from family.  

You could possibly gift it but that's a really gray line.

Two gifts that lead to better RE decision making. 

Both hing on having a gift (a real GIFTed) talent at selecting the tenants.