Cannot use commands as config values

I am trying to write my config file in such a way that it will dynamically obtain a colorscheme from pywal, by trying to extract the values from a file containing the loaded colorscheme, e.g. `border-color=$(sed '3q;d' ~/.cache/wal/colors)`. However, mako does not seem to support this, and the manpages make no mention of something like it, and I was wondering if there exists some mechanism in mako to achieve this, or if this might be a possibility for a future release.