Private money may be better. 

Just like doubling down on a bet you could lose it all. 

and the property had a private dwelling value appraisal much higher than the public property appraiser claims. 

pretty small hurdle to have a good win as a private lender just get paid as agreed.now equity participation loans those can spin the needle pretty well ..

Why not just advertise it as a 4 bed/4 bath and promote the apartment as its own private suite? 

I’m currently working on a deal in Fort Lauderdale & actively looking for financing solutions like hard money or private lending.

Since my firm is an investor private client boutique, I do not share resources outside of my client base.

I have heard of cabin / mountain market STR operators doing some kind of hiking package, or way to connect a guest to a private tour guide for an "upcharge" which gives the hike tour guide an income and the STR operator a nice upcharge too. 

Your best bet is to ask for referrals from professionals in the space: realtors, other investors, this forum, FB groups, etc.

NMLS does not regulate private lenders.