So it looks like I’m about 8 years late for this thread, but I found that I got quite a bit of front brake response before the brake light activated (I.e. the bike was slowing down without indicating to the motorists behind me that I was braking) and thought I’d share my solution.
Step 1 was to screw the front brake adjustment screw away from the master cylinder so that the lever was required to be squeezed more, and thus the little shaft that activates the brake light switch allowed to extend fully, before any front brake activation was experienced. However, this step alone resulted in way too much brake lever free play.
Step 2 (and I urge you to use your best judgement here, as this step is largely irreversible) is to file down the face on the brake lever which presses the shaft on the brake light switch in as the brake lever is released.
The most obvious concern here is that if you remove too much material, then the shaft on brake light switch might be able to fully extend and thus activate the brake light even when you’re not squeezing the brake lever. This could probably be mitigated to some extent by screwing the brake lever adjustment screw back in towards the master cylinder. On the other hand, for me it was kind of annoying removing the brake lever, filing, sanding, polishing (you want a mirror finish so that there’s no grabbing of the brake light activator shaft by the surface on the lever as it begins to depress it), and reinstalling the lever 3 or 4 times before I found I had removed the desired amount of material.
Another concern I had, though I’m not an engineer and am not sure how much of a concern this is, is that I imagine there’s a prescribed orientation, or angle at which the brake light activator shaft meets the surface of the brake lever which depresses it, with the aim being to direct as much of the pressure as possible straight down the center of this shaft, thus minimizing the amount of pressure acting on this shaft perpendicular to its travel in order to avoid damaging the switch. Whatever desired angle orientation there might be, it is likely that this will be lost without proper planning preceding the removal of material from the lever. I will mention that while I didn’t make overt efforts to address this, it was in the back of my mind and influenced my work.
Step 3 is to make sure all surfaces are properly greased and the lever reinstalled.
Step 4 is to test to make sure you have the desired brake light activation. For me, this was at the very end of the free play just before appreciable resistance from the master cylinder was felt. This allows me to give alert flashes as I approach some road hazard that I want to warn the motorists behind me of without actually slowing the vehicle.