scrlttr and non-window envelopes

First you need a minimal letter, e.g.

\documentclass{scrlttr2}

\begin{document}

\begin{letter}[foldmarks=false,addrfield=true]{%
    Markus Kohm\\
    Freiherr-Von-Drais-Str. 66\\
    68535 Edingen-Neckarhausen\\
    Germany
}
\setkomavar{date}{}
\removereffields
\firsthead{}\firstfoot{}
\setkomavar{signature}{}
\setkomavar{location}{}
\opening{}
\end{letter}

\end{document}

This would generate only the recipient address and the back-sending address. You may move the recipient address by changing toaddrvpos and toaddrhpos before \opening.

BTW: I'm currently working on a lco file that should do all the work—some future time.