Dual-render materials and lighting are go. The top two screens are both OpenGL renders from the viewport. The very top one is Solid drawing with Cycles, the middle one is Blender running in Blender Internal render mode. The bottom screen is a render from Cycles.
Thanks to BI’s much nicer OpenGL integration, I can have shadows in viewport now. Took not that long to set everything up (a couple of hours if that?) and totally worth it, I think. Tips and hints to follow later.