Ah yes. I had a similar problem in the townhouse I used to live in. The trees overhung the roof, and they had found a way inside.
First, find the hole and fix it. In my case they were getting through a place where the roof was separating from the framing.
Secondly, they make poisons which can delayed kill. It is a poison which is consumed and then activated when the animal drinks water. Since most water sources are NOT in your attic, you don't have to deal with the stink as they will most likely die outside at their water source.
Third, if you don't want to DoT them to death, your other option is to install a bright strobe light. Being nocturnal, they avoid the light and it drives them nuts. In the end, this is what I had to do. I never saw it because it was in the attic. Anytime I heard them, I plugged in the extension chord and the two huge strobes I had up there fired off, and they hauled ass.
There are several different options. Give this a good read:
http://www.bugspray.com/catalog/products/page359.html
Azorath