I have huge bottles of household cleaning vinegar. Do you think you could put it in the fabric softener dispenser? Guess that would be same as putting in during rinse cycleUsed them for a long time, but stopped a few years ago. Long story short: sensitive skin and bad case of allergies.
If you still need to soften your laundry, it's better to use a vinegar (a half of a cup during the rinse cycle will do the job) - it's natural, harmless and results are much better.