Use a sub-subject (here/reference) in a scrlttr2 letter?

Of course you can use setkomavar{subject} to add a subject to a letter you have created with scrlttr2.
However, many letters from official agencies or other public institutions do have another subject line. It goes like this:

Subject: Your request regarding XY
Here: Our answer that declines this request

This is especially true for official letters, official orders or so, e.g. regarding FOI requests.

Here is an real-life example in German:

The first line is the actual subject, the second one describes the content that is actually referred to in this letter, e.g. in a longer conversation.
So you usually keep the subject the same, but change the “reference” or however it may be called to indicate

I’ve searched the doc for scrlttr2 as best as I could, but could not find anthing regarding that feature. We can set everything, from date to (numerical) reference of the agency (“Your reference“ as yourref, yourmail etc.), but I want another subject line that is optionally less-bold than the original subject or so.
IMHO this is quite common.

How can I best do this?

Here is an example document that shows the two lines in the subject, at least:

documentclass{scrartcl}
usepackage{scrletter}
parskip3mm
parindent0mm % if you want to have no lineskip

usepackage{lipsum}
begin{document}
begin{letter}{Jerry Garcia710 Ashbury StSan FranciscoCA 94117}

setkomavar{subject}{%
    Subject: Your request regarding XY
    Here: Our answer that declines this request
}

opening{Bonjour elliot,}

lipsum

end{letter}
end{document}

It would be best if the first and second line could be styled totally separate to each other, e.g. first line bold and second line not-bold or vice-versa.

documentclass{scrartcl}
usepackage{scrletter}
parskip3mm
parindent0mm % if you want to have no lineskip

usepackage{lipsum}
begin{document}
begin{letter}{Jerry Garcia710 Ashbury StSan FranciscoCA 94117}

setkomavar{subject}{%
    Subject: Your request regarding XY
    Here: Our answer that declines this request
}

opening{Bonjour elliot,}

lipsum

end{letter}
end{document}