You can use a small metal 'rat tail' rasp or simply wrap and glue a spiral strip of sand paper around a wood dowel or steel rod.

I like to clamp the reamer in a fixed horizontal position and move the cork handle back and forth. It's easiy for me to grip the cork. Rotate the cork a bit on each pass to insure a round hole.

By adjusting your sanding pressure you can ream tapers as well as straight holes.

I use epoxy with filler to attach handles. The filler I like is made from light weight glass 'micro-spheres'. It adds strength, reduces the weight and makes it easier to apply.

I use 1/2" wide strips of drafting tape as needed for bushings. Leaving at least 1/2" between the tape bushings for glue. I mix the epoxy up to a very thick paste and coat all sides, as I assemble the handle I fill the voids with epoxy mix.