What are some effective "Guerilla' marketing tactics to help lease a Medical Office Building?

What's the occupancy?

How many square feet? What percentage is currently leased? Are you the tennant?
What is their TI allowance? Are you a CREDIT tennant?

You may want to market it to the dental market instead. Dentists are extrememly stable tenants, they don't move, and probably have a larger gross than their medical brothers and sisters.

When it comes to leasing a property, especially a property in a major urban market, such as Boston, advertising is key. I'd suggest a using a broker if you're not. Its worth paying the fee and getting tenants rather than paying debt service out of your pocket