Possible solution: cut the angle off an Allen key; weld to steel bar, say around 3/16" diameter, end-to-end. It doesn't need to be in perfect alignment, as long as it's pretty straight.
I've done this very successfully with a 3mm long-series drill bit. It's now about 16" long, and used for drilling down the middle of 6mm MDF, as used in dolls house floors and walls. MDF is weaker/less dense in the middle, so the drill doesn't wander much, and the holes let me run cables for light fittings.
I made a wooden jig: U-shaped piece of board, with two grooved blocks across each end of the U. Clamp bar down one side and drill t'other and push together in the middle. It helps to grind them to an oblique, so the joint is a 'v' you can fill with weld/braze/silver solder. If welding, preheat with a blowlamp to get a good joint (I used a MIG). When done, gently file or grind to get the joint fairly smooth. You could easily use steel studding (threaded bar), which is found in 1m x 6mm lengths from Toolstation, Screwfix, etc. Bend the end over in a vice to make the 'handle'.
It really is easier to do than explain, if you've got either a MIG set or a MAPP gas blowlamp (latter for silver soldering/brazing - you might get away with propane).
If you're going to try this, I suggest you make your tool first and test it for strength before committing to the design!
I've done a similar thing with a Torx screwdriver. One of our Philips cassette radios has torx screws holding it together, at the bottom of very deep holes. In that case the Torx shaft was removed from the plastic handle by heating it (and melting the plastic), then simply had some 8mm copper pipe squeezed round it with mole grips.
Looking back I should have welded it to some bar really - would've been easier to use.
HTH,
E.
Otherwise, I like the idea.
