easiest is to reverse engineer the signature details and craft packets based on the Sig RegEx for example.
For example, if a SIG is inspecting packets for "DNS" in traffic over 53/tcp, crafting a packet with this info will trigger the IPS...
I have used metasploit to trigger alarms in promiscuous mode, but not inline. It's pretty much the same though. Get metasploit working. go through the list of available metasploit exploits and choose one that is:
1) exploitable on the test machine
2) detected by Cisco IPS
Test the exploit without IPS. One you have verified that it is working(during my test, I was creating a local user on a Windows box), test the exploit with IPS.