Give this guy a try. http://www.nicks.ca/sanding.html
I have not yet used him but let me tell you a story.
I emailed him the other day asking for some sanding mops. This is what I got for a reply.
Sanding mops are meant to sand surface profiles not a flat surface in a hole. You need to use a sanding drum I think. The drum would also have to be smaller than the hole, probably no bigger than 2" or 2 1/2" in your case and 7" long so you can walk it around inside the hole. The other alternative would be something like a cylinder hone with 3 pads. Actually that would likely work the best. Make a cylinder from wood with a shaft in it that would fit your drill. I would use soft wood to keep the weight down for balance purpose, something like bass wood. Either cut slots lengthwise on four opposite sides or flats on four opposite sides and attach pieces of emery cloth using screws to secure them creating a flap wheel. In other words in order to sand a cylinder the paper/cloth must run parallel to the surface not at right angles as is the case with a sanding mop. Seems to me I have even seen some of the cheaper cylinder hones use emery cloth this way. Check with local auto stores or tool dealers
Hope this helps.
Any guy that turns down a sale for a happier customary is in my book.
So on his advice I went to tool making.
I took an old hone and knocked the stones off. Then I attached strips of maple with epoxy and rivets. Put some self stick Velcro on and no have a mug hone.
Second pic before honing
Third pick after honing for about all of 30 seconds.
Now all I have to do is get some hook & loop sandpaper. I used some stuff I had laying around to give it a test.