Different dynamic 1st and 2nd time in a repeat.

[Ritchie Fraser]

Hi all,

I would like to engrave two different dynamics for the first bar for the 
first and second time of a repeat.

Can't figure out how to achieve this. I have tried

\repeat volta 2 { a1\f\p |  a1 | a1 | a1 }

but the piano symbol is (a) not engraved or (b) engraved lower then the 
forte.

Any tips / hints gratefully received.

Thanks

Ritchie