I went to the hardware store and bought a short stump nose screwdriver and hoped that it would suffice.
I went back to my collection of random tools and foraged...
I came up with this quick and easy assembly which worked perfectly. Keep it in your idea bank if you are ever stuck between an exhaust and a hard place. If there is a specialist tool which you are able to just buy from any of your convenience stores, that doesn't always help. In Johannesburg here, there are only a select number of tools you can easily get hold of.
Make do with what you've got.
2 thrust washers.
2 small screwdriver bits.
Step 1: Assembly
The only confusion may be as to "why are there two bits?"
This is to allow for the washers to be forced against the parallel sides of the screw bits, whilst remaining parallel. You can imagine that if only one bit was placed between the washers, the washers would angle and the bit would easily slip out.
The images show the few steps of assembly.
Step 2: Additional notes
I could bond this assembly with Epoxy resin to create a more permanent tool, but the job is now done.
Not too shabby for a 40mm long Thumbsize Screwdriver.