engineer a frame solution so it becomes impossible for people to do this:
in all honesty i think you are doing fine with the current lineup.
either keep prices as low as possible, or offer as many colors as possible. i would buy a 725tr frame if i wasn't absolutely thrilled with my kilo. or, if the 725tr came in more colors, or if it was a little cheaper with the current color selection, or if it was lighter. i'm a lightweight so i don't need a strong freestyle type frame. i like aluminum bikes but i don't see people buying into a lot more choices, they already have a ton when it comes to steel and your lineup between the 20,21,25, and 35 is enough choice. just need more colors.