I sometimes find its easiest to grab a chucking reamer to clean up a hole
and spin it by hand. No, not gripped between my finger tips. LOL.
Occasionally I need to do something similar with a small drill bit. I've
used a variety of things. One that works, but isn't very easy to get a good
feel for is to grip the bit or reamer in a pair of locking pliers. I don't
care for it much, but right now there are two drill bits locked in locking
pliers hanging from the pegboard behind my tackle making bench.

Today I needed to use a reamer to clean out some rather longish holes in a
mold at an odd angle. I suppose I should have reamed them before I removed
the plates from the angle vise, but (a) I forgot, and (b) I figured the
drill bit that made the hole would have made it slightly oversized anyway.

So I found myself using a .126 reamer by hand to clean out a core pin hole.
I grabbed a small keyless chuck I acquired somewhere that has a 1/2" shank,
and used it as a bit holder. It worked great. It might have been better if
it had a big screw driver handle on it, but it was an order of magnitude
better than using some locking pliers to hold the reamer. Now I can make
such a contraption. It would be pretty easy. I've got three or four small
drill chucks that are pretty decent, but then I thought. I can't be the
only person to ever need to hand drive a small drill bit or a small reamer.
I would think ideally a 1/4" (6.35mm) capacity keyless chuck on the end of a
middle size screw driver would be ideal for this sort of work. Somebody
must have made one already. Maybe a 3/8 or 1/2 would be handy, but I
usually find myself dealing with this on the smaller bits and reamers.