Hi @dpkhm,
Thanks. So I had a chance to talk with the developers and after looking in more detail inside the code it is not possible to what you want to achieve as Variables are not supported inside value mappings.
From the code, it treats it as text so will not work.
Also, cross-referenced with the documentation and it does also say anything which supports Variables.
There was already a question on this topic recently on this post which seems to have the same answer by the member.