I seem to remember that I have "back bled" (non Harley)Front Forks in the distant past.
After replacing Front Fork Oil Seals, I put all the parts back together inc. Fairing. I then realised that I had forgotten to add NEW Oil to ONE of the forks.
Rather than take things apart to get into the Fork Top to pour oil in, I backflushed the NEW Oil using a GOOD/NEW cycle hand pump. This would be an easy way to replace the Oil without filling from the top. It was a long time ago but thats my memory of it.
Does anyone see any problems with this method.? Bungo

 

That is how you fill outboard motor gearboxes but the prob you might have is the lack of somewhere for the air to go as you add the oil, so it will pressurise the forks and it might spit back and get messy...the outboard has the level plug out to let the air bleed.

 

I seem to recall reading that is a way of doing Harley forks. Hopefully one of our experts will offer a view!

 

That is how I do them on my 1990 FLHS.

 

https://www.hdforums.com/forum/chass...ork+oil+change