Islam teaches us to recognize goodness in every human being and reciprocate kindness with kindness at all times.
You are therefore not only allowed but religiously mandated in Islam to speak about his goodness after his death. The fact that he was not a Muslim should never stop you from doing that. This does not mean that you participate in their specific religious rituals on this occasion.
So go ahead and give a eulogy...there is nothing un-Islamic about it. By doing this, in fact, you are letting them know the truth about our religion. In fact, I can assure you, it is through such acts of kindness and generosity of spirit that Islam spread throughout the world, and not through the sword and might.