Most PMC softwares allow this - if the PMC knows what they are doing.It's also just a one-time setup for the PMC!

Have you seen a positive impact in your STR besides the initial cost savings? 

Here are some specifics:Purchase price: $955KSeller Finance offer: 20% ($190K)Reno cost: $90K Ideally we would like to do a Morby Method where we purchase the home via conventional mortgage or hard money lender and on the back end have the seller lend us the $190K with a second position lien on the property and a 5-year payback.

Obviously aside from minor material cost savings the biggest reason is to save labor on all of the cutting in, which I feel would likely be moot with 3 sheens.

Even with an FHA, the work needed can creep upwards of similar or more than the closing costs, so you're looking at doubling your cost to own a multi-family property. 

I agree with Brian, it's a rare request and I can't think of many instances of seeing it in the last 20+ years of working in funds and syndications.Expectations are set up in such a way that most investors don't expect they're able to do this.

You could even look into Opportunity Zones.Other options are doing a Cost Segregation study depending on the property.To drag out the gains, you can do a Deferred Sales Trust, or Installment Sale.

I need to get the prop into an LLC as soon as possible and set up my RentRedi account/banking. 

The result is that the cost to add a hands off ADU is much greater than will be added by the ADU.  

@Francisca MacThere are many ways you can adjust all the settings… but the short “as it comes setup out of the box” answer is that there is no charge to a tenant to make a payment using a routing number and account number to post a payment.If the tenant opts use a credit / debit  card, there is a convenience fee charged for the use of the card.