Does anyone know whether it is possible to define custom ESCaliasESC'es in Mathematica? I figured that one could define custom keyboard shortcuts in "/usr/local/Wolfram/Mathematica/9.0/SystemFiles/FrontEnd/TextResources/X/KeyEventTranslations.tr" on Linux system, but many are grabbed by the frontend and cannot be redefined and one runs out of sensible possibilities pretty fast.
Answer The question has been answered here (thanks @cormullion)