Flexible Sanding sticks
1/4" popsicle sticks, 1"double sided foam tape, Auto grade wet/dry sandpaper..
Flip over and repeat
Trim ends and repeat on sandpaper
Trim to desired length
Simple, cheaper, effective.. this took 15 minutes.
For a stiffer sander, use tongue depressors, and instead of foam tape, use Contact Cement.
Cheers