[sr71]

Just an idea:
Make an offer of $10k (or less) if they leave the street. Do it behind a Lawyer, and let them think it's a group effort from other owners in the street. And write into the contract, not allowed to move into same suburb.
A big hit to the bank account for sure. But less than what the owner is going to add to the sale price, if you are asking to buy the property.
Invest elsewhere, and make the money back in that venture.
Good luck