Well if you don't want a big electric starter or a battery cdi, then you need a bigger arm. Sorry thats life
Most mags need 700+rpm to fire. Read the Zenoah instructions about prop placement vs mag. That might be enough to get you started. But a 5.8 is a big sucker and there is a lot of compression to slow you down.
There is no jump start for Sachs engines
Good luck.