I'm not sure if what you're looking for exists, maybe it does. What you're talking about is true constant-current dimming instead of PWM dimming like my driver uses. PWM works great for LEDs because there isn't any tint shift, but if you're talking about laser safety (I'm no expert here), it probably doesn't help because you're just delivering smaller pulses of the same high-power output.
Constant-current dimming can be accomplished by offsetting the current sense voltage, which can be accomplished by several different methods. If you only need two or three set modes, it isn't too bad because you can just bring different resistors or resistor networks into play, but if you want infinite dimming then you have can use an opamp to make and RC/LC circuit (rough DAC) to filter the micro controller's PWM signal into a usable analog signal which is then used to bias the feedback circuit on the buck or boost converter. It sounds easy, but it is hard to get one that works stable across the wide temperature and voltage inputs that you get in these tiny drivers, as well as the usual packaging issues. I believe that the LD-1 flashlight driver uses a similar method to accomplish its constant-current dimming (although it is a linear driver).
