Micro-Mark sells this
Basically, it is a jig on to which you place your hobby knife. It holds the knife at the proper angle to sharpen #11, #16, #2, and #24 type blades against a small Arkansas Whetstone.
They sell honing oil as an accessory for this tool. (For those of you who don't spend 50% of your lives sharpening things, honing oil serves as a lubricant that suspends the steel shavings from your knife and prevents them from clogging the pores of the Whetstone. In time, a clogged Whetstone will become ineffective. Whetstones should be cleared after each use by rubbing a liberal amount of oil onto the stone and then wiping off the excess with a clean cloth.)
I have yet to order one of these because it's hard to spend over $20 on a $2 knife, but my logic is poor. As their ad copy says, it should "pay for itself" may times over.
Has anyone tried on of these? If so, drop me a line or comment on this post.
I think this item is only offered at Micro-Mark: Hobby knife Sharpener