I've had people suggest putting Nitrogen in car tires for the same reason. Absolutely insisted it was a revolutionary idea. When I suggested that you can get the same result with air, and save on the cost of paying for a single gas, they were baffled. So, let me explain.
Air is about 80% Nitrogen.
Let's assume that every single non-Nitrogen molecule sneaks out of the rubber and only Nitrogen is left. From a starting point of 40psi, you would drop to 32. Refill the tire with air back to 40.
After topping it off, your tire is now 96% Nitrogen. (80% from the first fill plus 80% of the 20% you are topping off).
By the time you top your tires off a second time, you are north of 99%.
Paying someone to fill your tires with pure Nitrogen, assuming you have some way of vacuuming out all the air in the first place to get a pure fill, really isn't worth it.