So I figured out how to make and adjust a slur on my own. I am really wondering though if there is a more elegant way like how simple it is to do \repeatTie.
\version "2.18.2" \language "english" \relative c'' { \key d \major \time 4/4 \repeat volta 2 { d4 d8 d8~ d8 a4 d8( } \alternative { { e4. d8~ d8 cs4) a8 a4 a8 fs'8~ fs8 e4 d8 \bar ":|." } { e4.-\tweak control-points #'((-1 . 3.1) (3 . 3.6) (8 . 3.4) (10 . 1.5)) ( d8~ d8 cs8) fs8 fs8~ } } }