Hi Robert,
Well, I don't have 2.18, so I don't know if this is available to you, but if you can use the openlilylib bezier shaping code, you can have very fine control using the \shapeII function.
\version "2.19.48"
{
\time 2/4 \key des \major \omit Staff.TimeSignature
\override Tie.minimum-length-after-break = #13
\shapeII #'((() () () (-0.6 . 0))
((0.9 . 0) (p 20 0.4) (p 20 0.4) ())
) Tie
ges'2~ | \break
ges'2
}
This is far more tedious than Pierre's solution, but it sure works and you can tune it to the approval of your professional engraver friend!
Andrew