contact senior lender or trustee if you can, tell them your a junior in possession and ask them to post pone the sale for 90 to 120 days so you can do a refinance on it.. 

Unless the land had such a signifacant value like over $500K you might find a private lender to put a junior lien against it if you own it "free and clear".I have seen some private lenders offer a higher LTV even 100% if the collateral is sufficient, but again land is tough to resell unless its commerically zoned in a great location.  

It's actually a great idea, but one you may want to wait until Junior year of college to do.

DSCR requires No income, No Taxes and Commercial requires a PFS, occupancy ratios usually above (90%), Credit scores above 720+ much higher assets for (PITI reserves and overall risk, landlord seasoning, and more.A Heloc can be used in most cases for anything but when you are trying to buy a commercial building which is higher risk, the committee/UW can and in most cases will deny it if they feel you are over extended low assets or with no landlord experience, unless you have a meaty amount of equity to cross collateralize for a junior lien on another property.

Technically the HOA foreclosure was invalid but that is a completely different issue as you never go off tax record to see who owns a property you go off of recorders office and depending on state have to list junior liens in the complaint. .

The more junior sponsors are seeking more of the first two bullets; but fortunately you're also yield-seeking as a non-accredited investor so there is alignment.  

Recognize that in California, single family homes can add one detached ADU and one attached ADU or junior ADU.

Previously I had learned about junior mortgages, but Dean's course focused on first mortgages, which I did not have any experience and are a different animal than seconds or junior liens.

Based on your numbers, do you have a general idea of the total valuation of your entire property prior to and after the junior ADU? 

Generally most mechanic lien and any lien that is junior to the foreclosing entity will be wiped after foreclosure.