I wanted some socks I could wear with my flip flops since i live in flip flops. At the Epcot Japan store they sell them.
1. Put on a pair of socks and either measure the length needed to cut in between the big and next toe or go ahead a carefully cut as deep as needed.
2. Reverse sock (pull off) so it is inside out.
3. Carefully sew the area you cuts so that it would form a area for the big toe to go and an area for the rest to go. Sort of like a V shape. (I hand stitched mine and double stitched it, I recommend this to insure they can last through lots of use)
4. Turn right side out and try on to make sure they fit, All Done!
I made one pair (tester) for myself and one for my husband. I would test out on an old pair of socks unless you are super comfy with sewing.