Tie collision with note

[Nicholas Moe]

I am working on engraving an organ piece, César Franck's Cantabile. In
the LH in mm. 16–17, the middle voice is tied, but the tie collides
with the notes in the upper voice. Ideally, its shape and position
should match the tie in the upper voice, only shifted down. How can I
achieve this?

Here is the tiny example:

% begin example

\version "2.13.54"

\relative c' {
\clef "bass"
\voiceOne
<<
                { d1~ d2 c }
                \new Voice {
                        \voiceThree
                        \shiftOff
                        a1~
                        \shiftOn
                        a2 g
                }
                \new Voice {
                        \voiceTwo
                        d2\( f
                        e2 e\)
                }
>>
}

% end example

Thanks,

Nick