The strap on my bike light ripped, which made the attachement to the handle quite unstable and it kept getting pushed back and forth.
To strengthen the attachment, I designed a replacement clip, that can be fitted to the original underside of the bike lamp. You might have to adjust the size of the clip according to the circumference of your bike handle.
You'll need the original screw from the bike light to attach the parts on the top and can then use two M3 screws and nuts to secure the clip around the handle.
No need for infill, just lay the parts flat on their sides.