I know this is a bit more than you were thinking, but it might not be too hard to put together a PWM controller.
A POT, microcontroller, and a couple of FETs can do the trick. Sure, there is a little more to it than just that, but once you understand it all it isn't too bad. If you wanted to skip the POT you could simply have the microcotnroller ramp up the duty cycle to help limit starting current spikes.
Good luck with whatever you figure out.