I have these kind and this is what I did. The same would work for the regular crocs as well I'm sure.
This style comes with a bow, so the turquoise part was already on there. All I did was just put some ribbon around it the other way:
That way I could use an alligator clip and just slide it through:
And wa-la! Simple as that. The only problem is you have to have the shoes in order to do it this way...I had a lady send me some loafer type shoes that had ribbon threaded in them. I rethreaded them and did it just like this so she can interchange her bows. It just makes is SO much easier!