Brainstorming a possible way to make a tool, aren't the outside wrenching surfaces of an injector 27mm hex-shaped? You got an old/bad injector? If so, you could try disassembling the injector and sacrificing the lower half as your 27mm allen drive tool. You could either grab onto it with some big vice grips or pipe wrench, or maybe weld or grind on it to adapt a ratchet type drive.