If they have a power rack at your gym, set the J hooks at the same level as a normal bench stand, set the safety bars just below chest level, and then drag over a flat bench from the dumbell section of the gym.
Benching this way you can roll the bar back off your chest to just above your neck or to your waist on to the safety bars, assuming they are smaller than your chest.
I do this at home in my power rack and it works fine.
I rarely ever go to complete failure, but when I have, I have safely been able to get out from under the bar with no spotter.
Or, as others have said before, just grab a trainer, gym employee or another person working out to give you a spot.