Hi @David Miller, it appears that would be the route to get some "skin in the game".

I would ask the lender, but probably not most lenders want you to have skin in the game, even the seller takes on a lot of risk if you don't pay, because they would not be first loan position. 

They have more skin in the game then you do.Make sure you get clear title.

I always make sure I have some skin in the game.I think this is most definitely the way for you to go.

I hope I never have to do that but just curious as to how difficult is it.

Has to be the right fit of course and both partners need to have some skin in the game but win-win all the way.  

I was trying to consider some factors that may come into play - from what I understand you can put as little as ~3.5% down under an FHA loan - will it be more beneficial for me to put "more skin in the game" with the largest possible down payment I can make (say, closer to 10-15%)?

You usually have to have some skin in the property in order for them to lend to you.

I am having difficulty deciding whether I should sell my home and try to purchase 2 properties or use a HELOC to purchase my next place.

Even an hour adds complexity and difficulty arranging things and costs a lot in fuel and time if you self manage .