The dropper outer is a mare to feed through, but as long as its just the outer and not the inner cable thats damaged you can inch it back or forward past the motor to leave enough in the seat tube to reach the seat post. You might need to inch it up the post to start so you can get it connected to the post, then inch it all back down slowly (without disconnecting from the post as youve experienced already!).
Also, if you are on a 20mph limit consider changing the chainring to a bigger size, running in high gears will wear them out real quick and leave you with hefty and regular replacement costs. Ive just left mine at 15mph cut off for that reason and cruise at the motor limit, I dont feel a real need to go faster on flat stuff given its the motor thats getting me to that pace anyway, so just go at the motors speed.
Also, if you are on a 20mph limit consider changing the chainring to a bigger size, running in high gears will wear them out real quick and leave you with hefty and regular replacement costs. Ive just left mine at 15mph cut off for that reason and cruise at the motor limit, I dont feel a real need to go faster on flat stuff given its the motor thats getting me to that pace anyway, so just go at the motors speed.