Actually the role of the godparents functions mainly within the sacramental ritual, in which they are asked in the child's behalf ia:
Do you accept the duty of raising this child in the faith that he/she might keep the divine commandments and love God and fellow man as Jesus Christ taught us...
Do you renounce satan and all his works....etc., etc.
To these and a litany of other questions he answers the Polsih equivalent of "I do!"
(Jesteśmy tego świadomi...Wyrzekamy się...)
Other than this there is no specific role the godparents have to perform. At the christening party the godfatherr could raise a toast to the health and wellbeing of the newly fledged Christian, his aprents and family, but that is purely optional. If he is not the eloquent type, he is not really expected to say anything.
Polish Christening parties are very formal. once all the guests have arrived and a light appetizer has been served...the DJ or band member asks the godparents to go up to the parents and the baby and each godparent usually will say a blessing for the baby, parents and guests.
what's an appropiate blessing to say...not to long and not to short.
Perhaps something like this might do:
Dziś mały Kamilek (Andrzejek, Wojtek, Józio, Klimuś...) został pryzjęty do naszej wielkiej katolickiej wspólnoty. W imieniu nas wszystkich tu zebranych, jako jego ojciec chrzestny, chcaiłbym mu życzyć, aby jako dziecko Boże rozwijal się w sile, zdrowiu i wierze, na pociechę rodzicom i na pożytek współbliźnim. Amen!