Unfortunately, I give it up.
The solution I come up with is the following:
We use 2 separate profiles - 1st is main site profile, containing settings such as language, timezone and other site specific things as well as link to Discourse Profile and - 2nd - Discourse profile itself without any changes.
I still hope to see described solution, but understand that it’s pretty hard to develop correctly, so two profiles seems ok for us.
If you want to investigate this, I can try to help (I’m not a Ruby pro, but can help with JS maybe:) Let me know.