MakerLab Lithophane Lightbox cable grip / plug

The MakerLab lithophane lightbox frame has a hole at the back to allow for a USB plug and cable to pass through.I didn't like the big gap and also wanted something to grip the cable so that it didn't get pulled out. This model both bungs / fills the gap, but also grips the cable so that it cannot be pulled out.Please excuse the poor photos.