Maybe give them a bottle of wine and a nice dinner gift certificate to them.
I guess it depends on how much time they have spent with you and how
much time they have spent in preparation.
You can also be the first to recommend your friends and family to that agent, especially
when you know of buyers and/or sellers.
If you ever move out of that house, tell the realtor first and give them the contact information for the landlord.
That way they can have first shot at getting the listing.
Agents know leasing contracts to protect you as a client... is this an "office supply lease agreement" If so I would be extremely careful.
One of top 10 questions I answer daily HOW a family leased a property without an agent loss of their deposit, problems and etc.
FYI - if you have problems with property owner during term of lease WHO is going to protect you?