HELP: I have half the down payment on a killer deal

So I need 25% down on a huge building that cash flows incredibly well. I have about half of it. It's a 5 unit plus so I need a commercial loan which has tougher lending rules.

Bank lending rules won't let me borrow the rest of the downpayment, I believe. So how do I still do this deal? I know I need adequate reserves, etc., but I have the ability for more than enough reserves from an untapped HELOC.

Sorry for the duplicate: I posted this in tthe wrong place and can't figure out how to delete the other post.