repeat with different dynamic - midi output

[Gianmaria Lari]

I have something like this:

frag = { \repeat volta 2 {c'^\markup {p (2nd time: f)} d' e' f'}}

\score {\frag \layout{}}

\score {\unfoldRepeats \frag \midi{}}

As you can see I mentioned in the markup that the first time the score should be played piano and the second forte. Is there any way to write is as a true dynamic and make lilypond generate a corresponding midi?

Thank you, g.