Used to be you could buy like diodes or rectifiers that fit into the socket in front of the bulb. Turned the AC into a pulsed, more smoother DC and supposedly gave the bulbs a much longer lifespan.
I seem to remember you could get them through Edmunds Scientific or some such... I used to get tons of stuff from those guys when I was a kid!
I never tried that. But a dimmer even slightly dim might extend life somewhat also.