I don't know much about this particular build but your solution of putting a 6-pin connector onto the other end of the Air cable (see photo) seems reasonable. If you already have a spare 6-pin connector and pins then you can just solder them on and slide them into the plastic connector plug. If you don't have a spare 6-pin connector then you could cut off and solder on the 6-pin connector from the supplied cable, and protect the joints with heat shrink.
Another solution would be to solder in some extra lengths of cable into the middle of the supplied cable. I already have
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all the kit required, soldering station, solder, heat-shrink and the soldering skills to do it, because I build a lot of racing drones. With either method, pay very careful attention to getting all the connections right - but it shouldn't be to difficult as they are parallel cables, as far as I can see from photos online.
If you don't have kit for soldering then maybe you have a friend or acquaintance who can do it for you - or can even take it to a hobby shop to be done?