Tweaking ties in single staff polyphony

[Patrick Schmidt]

Hi all,
how can I tweak the form of a tie in one voice in order to avoid a collision of 
the tie with the notes of another voice of a single staff polyphony? I do not 
merely want to move the tie position but bend the tie to almost achieve a 
semicircle above the noteheads of the other voice.

Here's the problem:

\version "2.12.2"
\relative c' {
        <<
                { \time 2/4 bes2~ bes } \\
                { r8 <f' c ges> r <f c ges> s2 }
        >>
}

Thanks for your help

Patrick
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