There are a number of blogs/posts on the BRRRR method, which takes advantage of the cash back refi and Bigger pockets also wrote a book on the subject (also available on audio book) the book does a great job of breaking down the pros and cons and walking you through the process. 

Flipping is another case -if all is done in the tax advantaged account IRA/401k- buys the property, pays the contractors, sells the property and files the 990T irs UBIT tax return.

I generally think it is better not to use your tax advantaged plan for your first RE deal.

A couple of questions come to mind-Are your tax advantaged accounts operating as a business and paying UBIT?

That being said, with the Covid-19 virus and so many people out of work, having section tenants is a real advantage. 

So honestly I was hoping that someone here had taken advantage of this before, and could advise. 

We wouldn’t be good businesspeople if we didn’t try to take advantage of that and recoup our current loses.

I would figure out an asset class or location that gives you a unique advantage, www.adventuresincre.com is a great resource for modeling among others

So I would like to take advantage of that.

That capital basically becomes illiquid as long as the loan is outstanding, I'm not sure I see any advantage over cash.