24-105 with Extension Tubes or Diopter Filter?

7D & 24-105 f4 .... should I get extension tubes or diopter filter?

I want to get shots like below (if possible - without having to purchase Macro lens):

I did some tests with various lenses and tubes, the 24-105 was amongst them (http://www.zen20934.ze​n.co.uk …LensTests/Macro​/index.htm there are some 100% crops), it worked fairly well except for the corners which may just be sue to curvature of field.

There is a table of the theoretical magnifications and working distance with various tubes here http://www.zen20934.ze​n.co.uk …o_Equipment.htm​#Extension Tubes.