tying notes across voices

[Shuwei Hu]

Dear list,

I'm trying to tie notes across voices. Example:

    \version "2.20.0"

    \relative c'' {
      \time 3/8
      << { d4 b8 } \\ {g b g} >> |
      <<
        {
          r8
          \tweak Stem.transparent ##t
          \tweak Stem.length #8
          b8~ b\noBeam
        }
        \\
        { r8 b8[ g] }
      >>
    }

The second bar uses a trick of invisible notes copied from the 
documentation<https://lilypond.org/doc/v2.20/Documentation/learning/other-uses-for-tweaks>.
 The same trick fails to apply to the first bar because the note d4 occupies 
the space for the invisible note.

Does anyone know how to tie notes (b8) across voices in the first bar?

Any help is appreciated.

Best,
Sylvain