+1thanks for the advise, but it will be mostly for outdoor fill. will the 100m canon macro lens on the 5dmk2 get too much in the way for macro? or is the flash high enough?Shouldn't you be looking for a macro flash in that case? Or a ring flash?
OR, you could look into getting a couple of cheaper third party speedlites and a radio trigger, which will allow you position them wherever you want.