Their borrowing rate is 30-50%!

Just depends on the lender, but sure...I have blanketed loans across multiple properties and collateralized loans before...if your lender is good, and you are a qualified borrower, your lender should have lots of options...just ask.

Likely, it will be at 3% or so, which means you use their money at 3% while your policy earns 5% and you'll go make 25% with the borrowed money on a flip. 5) guarantees to never lose money (there's reserve requirements to back your accumulated money)Happy to explain this more privately... there's lots of details there.

You can borrow money from friends and family2.  

That LLC will be the "borrower" and the guarantors on the loan will be your marketing company and you personally.

I could take out a Home equity loan from one of the properties to purchase the next one, but I would prefer to borrow the money and finance it over a five or ten year period.

@Peter Ledger, Yes(ish) I'd have to look at what the deal and the borrower looks like too many variables to give  strong opinion. 

Marketing is a cost of doing business that same as having an office, borrowing money, etc and there is never a guarantee of success. 

The other thing that would happen here is you would be liable for the taxes on the profit of the flip, it sounds like he may be trying to avoid that as well.This sounds like a Straw Borrower situation to me.  

Once upon a time there was a borrower who took ill and gave his daughter power of attorney.