I think you need a make-up air unit interlocked with the exhaust fan. The design is a mechanical trade problem, so I'm not sure of the rules.
Recently, I interlocked an exhaust fan with a furnace and the furnace had a large duct on the return air side that drew fresh air from outside. They were using the furnace as a make-up air system. A heater was installed in the fresh air duct, because cold winter air can damage the furnace.
Unless your furnace draws air from outside, it won't solve the negative pressure problem.
