Tools and materials:
6 inches or so of rhinestone trim
Pliers w/ wire cutters
Earring posts and backs (or clip-on earring backs)
Super glue
A toothpick or paperclip

Cut off two pieces of trim, two stones long, from the chain using wire cutters or pliers.

Put a blob of glue on the earring back. Stick the two pieces onto the glue and earring back. To keep the earring stable while freeing up my hand, I pushed the earring post into a cork.

Wrap the chain around the square of stones, measuring how much trim it will take to circle the four inner stones. Trim the chain down to that size (for me, it was nine stones long). Using a toothpick or wire, dab glue around the outside of the square. Press the newly cut chain into the glue, around the sides of the four original stones. Press the earring flush against the cork (so the trim is supported while the glue sets), and leave to dry.