Personally, I think you are straining at a gnat here. IF you gain anything, it will be minimal, and require a lot of work to get there, and you still won't be quite sure.
If you want to shift the bias to the rear a little, you can put more aggressive pads in the rear and not the front. But, since you are looking for improved performance, I still say just go with more aggressive pads all the way around, or upgrade the size of the system overall, either w/ the CSVT or FSVT brakes or bigger, like Todd TCE's Wilwood kits, etc.
It's almost like spending $750 to redesign an intake manifold to make more power, when a $1000 supercharger is legal to run and makes way more power. Further, bias is a dynamic thing, the necessary proportioning is constantly changing due to vehicle loading, cornering loads, road grade, pad types, road surface conditions; and a ton of other things. OEM's spend months and months of time and hundreds of thousands of dollars determining how to set up valving on a new brake system to cover everything. You will never hit all the conditions, and when you run into one you missed, and you snap oversteer into a tree . . . its a bad thing. Leave the proportioning alone until its a fully gutted and caged track only car; OR you have dramatically changed the brake system, and the new parts weren't designed to work w/ the stock valving.
