Add rhythms above the staff

Please note that this is an English forum, so either try to ask in English (and promised, we won't laugh at you, many of us are not native speakers) or ask in the French forum, http://musescore.org/fr/forum/15.

I tried Google translate on your post, but it didn't make the question clear enough to me to be able to answer it.

Attacher un exemple serait le bienvenu afin de pouvoir définir quelles fonctionnalités de MuseScore seront pertinentes, car, honnêtement, je ne vois pas trop ce que vous voulez faire...
( Pour cela voir "Fichiers attachés" dessous la boîte de dialogue pour joindre l'exemple ).

Attach an example would be welcome in order to determine which features of MuseScore will be relevant because, frankly, I do not see what you want to do ...
(For this see "Files attachments" below the box to attach the example).

I would just add these as normal ites just above the staff and flip the stems up. Or, if you want regular notes below, add the rhyhtms in voice 3.

Here is how I would do it:

Create the first note as a G above the stave.
Enter the other notes (all G's).
Double-click on each note in turn and press the Up Arrow key three times.
Select all notes and turn off the beaming (if this is how you want it to appear).
Flip all notes vertically with X.

One advantage of doing it this way is that you can easily enter lyrics.