Understood… there is not an easy solution that I’m aware of for this situation.
If the new layer is only for one detail, I would create a copy of the file, and would add that new layer in the new file. Doing that, you can maintain all your details in the old file and use the new file for just that isolated detail. I know this is not what you are looking for, but sometimes you have to find dirty workarounds.
I really don’t understand why is taking McNeel so long to give detail layers priority over model layers, it’s been asked so many times… Just lets us turn layers off in model space while being able to turn on the same layers in details.