My wife purchased her house in 2009 with the assistance of a program by the county. The deal is that if you qualify and purchase a house the county pays for half of the mortgage price and you don't have to repay them until you sell the house or move out. So for example you buy a $100k house, the county pays $50k, and you get a mortgage for the remaining $50k. You don't have to pay the county back as long as it's your primary residence.
So I entered her (now our) house in mint, and originally I manually put the price of the house less the $50k we will owe the county eventually. The price of our house has changed though, and rather than constantly updating it manually I would like mint to automatically pull the value from zillow. I can't figure out how to make it account for the $50k we will owe the county though. It won't let me add a real estate item with negative value. I also can't enter a fictional 0% loan without linking it to a real account. So how do I account for this and have it update my net worth automatically?