Reply by Loren

A router base makes the cut tricky to work out. You
can build a custom cradle to hold a router without
the base flange getting in the way, but you’ll still
need a real long bit and probably a collet extension –
you’re looking at over $100 for those two tools
and the there’s the fuss with making the custom
router table to do the cut.

A simpler solution is to work out a way to drill it
with forstner bits on a drill press and knock out
the waste with a chisel. Not quite so neat, but
quick to set up and the chisel work is easy.