You can send an insteon command to a button referencing the added device.
Take a look at the thread below for how to add the separate buttons as devices. Let me know if you still have problems.
http://www.simplehomenet.com/forum/viewtopic.php?t=329&postdays=0&postorder=asc&start=0
From the thread, the steps are
1) Go to add a new device
2) Select a new group
3) Enter a name
4) Hit save
5) When prompted to add a new record, say yes
6) The EZSrve will go into linking mode, press the corresponding button on the KPL you want linked for about 6 seconds
7) The EZSrve will say it found the device and stop linking.