a close-up lens should suffice:
http://www.bhphotovideo.com/c/product/10183-REG/B_W_65076665_77mm_Close_up_NL_5.html
The 24-70 has a minimum focusing distance of just 38cm. This one or a +3 should get you the result you want.
http://www.bhphotovideo.com/c/product/10183-REG/B_W_65076665_77mm_Close_up_NL_5.html
The 24-70 has a minimum focusing distance of just 38cm. This one or a +3 should get you the result you want.