What you need:
Bare Paint Pen
Heat Gun (if you’re impatient)
Hot glue gun (if you don’t have thick cardboard)
Take a piece of cardboard large enough to draw 2 lines 12 mm wide and 75 mm long.
Draw two lines about 70 mm long 5 mm apart starting at the edge of your cardboard.
Paint over the these lines with the Bare conductive paint pens making each line about 1 mm thick making sure they do not touch
Cut the cardboard out so it is thick enough to fit snuggly in your USB port (or hot glue several pieces of cardboard together) and about 75 mm long. **Check to make sure that it fits into your port.
Put the LED on top of the two lines and put more Bare paint to “glue” it down.
Wait 10-15 minutes for the paint to dry or use a Heat gun until the paint is no longer tacky. Be cautious that the paint will expand when heated.
Insert your LED/cardboard USB into your port and watch it light up!!