First, establish a connection with your negotiator.
An effective salary negotiating tactic is to create a personal rapport with the other person. Whether you’ve been working together for a while, or just met them, take the time to establish your personal relationship.
You’ve got to develop, in whatever amount of time you have, a degree of personal empathy with that person, some kind of personal connection with the individual so they look at you as other than something like a cog in a wheel.
You’ve been talking with them for a while, they like you, they’re offering you a role, so begin building a personal relationship beyond just the job, or the interviews. Make sure you’re able to connect on something deeper and beyond just your professional relationship.