You can charge the tank easily and it will have the same effect as a bladder tank of the same size. However, you will have to maintain the air in the tank.
Turn off the breaker to the pump. Run all of the water out of the tank. If it is waterlogged, you may have to work a bit to get it all out. Here is a sure way.
You need to add a port to the inlet pipe, or to the side of the tank if there is a plug in the side, to admit air to the tank.
Put air in the tank to about 2 psi less than the START pressure of your pressure switch. Then run water until the WATER is all out of the tank. Then add air again as necessary to 2 PSI less than the START pressure. Turn on the circuit breaker and let the pump fill the tank with water.
When the tank is full, figure out how full it is of water by tapping the tank or noting the cold water level. Mark the tank at that level. When you notice that the water level at shutoff is higher than that point, add 5 PSI of air to the tank, above the pump shutoff pressure. Check after a day or so and repeat as necessary.