[Dev-luatex] Start LuaTeX with Lua only?

Ok, this is actually kind of stupid since Taco and Hans are sitting right before me, but we are in the middle of a talk. Is there a way to start LuaTeX with just a Lua file, but have this Lua file feed TeX input to a TeX process, via tex.print or similar? Or do we always need to have a TeX file which does some \directlua call before we can have Lua feeding TeX input to a TeX interpreter? -- David Kastrup