Your first post confused me.
You said there was a bug, (without further qualification) and went on to say, "It is such a important feature. I cant show it to customers without the custom styles showing in the styles list."
So that wasn't the issue at all, as you know you can show any Editor instance to your customers with the custom styles showing in the styles list.
The post you referenced proved it.
You should perhaps have asked about saving an instance with custom styles as a preset.
The "I can't show it to my customers . . . " bit was irrelevant in the context of this post (being untrue).