Just as an idea, could it be possible to make a miniature version of the WWII C Coffman Starter for a HT engine?
From wikipedia "The Coffman engine starter (also known as a "shotgun starter") was a starting system used on many piston engines in aircraft and armored vehicles of the 1930s and 1940s. The Coffman system was one of the most common brands; another was the Breeze cartridge system, which was produced under Coffman patents. Most American military aircraft and tanks which used radial engines were equipped with this system. Some versions of the Rolls-Royce Merlin engine used in the British Supermarine Spitfire used the Coffman system as a starter."