tie with manual repeat

[Gianmaria Lari]

I have the following code 

\version "2.19.82"

\fixed c' {

  a1~

  \set Score.repeatCommands = #'((volta "1")) a2 b2 \set Score.repeatCommands = #'((volta #f))

  \set Score.repeatCommands = #'((volta "2")) a1^"Fine" \set Score.repeatCommands = #'((volta #f)) \bar "|." 

  c1 _"Da capo al Fine" \bar ":|." 

}

with this output

How can I make a tie also on the "a" in the second alternative?

Thank you, g.