I searched for plugins that might do this for me, but finding none, I wrote this one
https://github.com/EasyG0ing1/SoloFolder
In Deluge 1.3, use the py2.7 egg file and install it through the preferences pane. It will work just fine.
For Deluge 2.0, use the py3.8 egg file and copy it manually into your plugins folder
~.config/deluge/plugins
then restart deluge and your UI, then go into preferences and enable it.