I find this funny that you call it a problem, for most a thin bone structure is a blessing. The smaller your bones the bigger your muscles appear. Take a look at Flex Wheeler I remember reading a MuscleMag that described him as having bird joints. Your real problem is your very ectomophic concentrate on low reps and heavy weights this will create muscular hypertrophy "widening of the muscles". To answer your original question you can't enhance bone structure but through power lifting you can give the appearance that you did.