This is a great idea, as it really really bugged me not being able to have macro photos. I wouldn't try and take my iphone apart but it gave me an idea to use a small manifying glass I had as below.(I found this in a childrens science kit. - Couldn't get a macro photo of it for obvious reasons)
The miniature magnifying glass next to a British 1p piece:
And some pictures taken on my iphone with and without the glass:
MCE Remote:
Without
With
Trident Chewing gum:
Without
With
Watch:
Without
With
The point is, it's clearly a very simple solution. You need a better focused lens. If you can find anything to take the lens out of, perhaps you could put it in a holder or attach it to your iphone case somehow in a removable fashion to give you "macro" shots. I for one will carry this little magnifying glass around until i work a removable alternative. Great idea. THanks for hte heads up.