Steering with your knees is nothing unusual. Telescopic type of tiller is straight and requires additional fixture to be grabbed by the knees. This is just another idea of how it could be done. This piece od DN jewelery is 3D printed with carbon fibre filament making it very strong and super light with only 34 grams (1.2 oz).
This particular fixture is designed for 25mm (1 in) in diameter tiller pipe but can be customized to any desired cross section.
Email me for details.