Some keyboards have these limitations. The best thing to do is try and find a section of your keyboard that can be pressed simultaneously and then change the keyboard key layout to match.
It would be quite difficult to set this 2 chord max setup as it would need it's own scores and would need to be quite inteligent to make thegame feel right. You might just be better off playing in the lower difficulties as they will have less chords and are charted correctly.
i view this as a negative feature for the project so dont see it happening, its basically a cheat that results in fragmenting the game just to enable a controller to partially function for a limited gameplay experience, its no substitute for picking up a fully functional controller be it an instrument or simply a better made keyboard