A guy at the range has hands like blankets and he can touch his thumb to his index finger gripping around a double stack para ord .45 1911. Same on a fullsize HK. It's retarded. he bought a G17 L and had your same problem so he simply added marine tex to the grip [mostly the front strap and sides] until it was a nice fit. then he shaved it down to custom fit his grip, finger grooves and all. Nice stippled texture loacks it in good. Not that I can even grip it. It's like shooting a coke can. I'd try it out because then you have a custom glock grip. Plus I love arts and crafts on guns.
-chris