I use two mice on my Gentoo box due to few good reasons. Trying to get them to work all the time took some time though I am not sure if that's because I am too stupid to make them work together.
Anyways, here's what worked for me:
~ # less /proc/bus/input/devices
Find the line that says "Handlers" below your Synaptics and the other mouse.
Recent comments
1 week 1 day ago
2 weeks 23 hours ago
2 weeks 1 day ago
2 weeks 4 days ago
3 weeks 6 hours ago
3 weeks 2 days ago
3 weeks 2 days ago
4 weeks 21 hours ago
4 weeks 6 days ago
4 weeks 6 days ago