Step 1: Get a Cheap Canvas
Depending on the amount of sunglasses, select a canvas size. The quality of the canvas doesn't really matter so make it a cheap one.
Step 2: Paint Something
I never painted in my life, so this part was a risk for me. I took a rayban shape of the Internet, made a cutout and use a metallic copper spraypaint for the glasses, the rest is basic acrylic paint.
Step 3: Fortify
To keep the painting from disforming, i fortified the back with duct tape, before cutting.
Step 4: Slice
Take a ruler and slice some rows, aprox 18 cm apart.
Step 5: Hang Your Sunglasses
The end result