Tieing into two voices

[Sebastian Menge]

Hi

I would like to tie a note into a short polyphon section

\score {
   \relative { g2 ~ << g2 \\ {\stemUp c8 d e f}  >> }
  \layout { }
}

But that gives a warning and no tie. (It is intended to have two half notes tied)

I could extend the polyphony and use silence but that doesn't seem right and would clutter the source.

Actually the one voice continues and just for some bars/beats another voice sits on top.

How can I realize that?

Thanks, Sebastian.

Background is some modern organ music, there are many occasions of this "problem":