So you are talking about the length of the rubber covered pin you put your toe under on the shifter, and the width of the brake pedal pad your foot pushes down, correct?
Not the actual length of the pedal or shifter from their pivot point?
I have currently been looking for a similiar solution, as I am back and forth between 25 and 40mm drop pegs for my Gsxr1k.
I don't have the shifter clearance problem of the Gen3 Busa, but as you say, the drop peg will push both feet out slightly wider.
I have been looking at cheap rearsets, and combining drop pegs.
Some of the rearsets have flat bars for the shifter and brake pedal arms, and the tips of each thread or bolt to the arm, so wider arm tips could be machined easily.
I would like some quality rearsets too, and plan to eventually, but I would rather hack and mod a $70 ebay china copy first, in the hopes of coming up with the right comfort and clearance.
I know an inch to 1.5" drop will have them dragging corners, lol.
If I find anything aftermarket than has potential, I'll post it here.
And I am activel looking for the best solution...as my knees Really like the drop.
Good luck with your search.