How to work a friend's money into a deal

[Nathan Estochen]

Hey BP,

I'm looking for my next multifamily to owner occupy and am limited by my income and prices in the area - but need to stay somewhat close to Boston, MA for my full time job. 

I have a close friend with a large amount of cash who wants to lend me money to speed up the rate I can acquire properties. The plan is acquire 10+ unit multi's in the future but I need a place to live in the short term and thought this is a good way to get their toes wet with involvement on a first deal - a sort of proof of concept.

For this particular deal I'm still interested in bank lending and would use the friend's money as a down payment to increase the variety of locations I can buy.

My question is what are ways around the fact that a bank would not see the friend's money as a legitimate down payment, but as another form of a loan? How does my friend need to be worked into the deal for the bank to honor it? Co-sign? 

Thanks,

Nate