Here is a lovely little piece written by Hector Berlioz for Harmonium (l'orgue melodium) in 1845.
It is quite simple and I use the foundation stops of the Positif and Recit as there is quite a lot of change in volume required. It is obviously a harmonium work as there are seperate volume indicators on bass and treble, which aren't possible with the Swell of the organ. I did my best to give a sense of what Berlioz was aiming for, without playing with literal followings of his dynamic markings.
Hope you enjoy.
A link to the score: http://imslp.nl/imglnks/usimg/2/20/IMSLP58508-PMLP119998-Berlioz_-_Hymne_pour_l’élévation.pdf