Although the tool currently does not support configuring the source router, you can however change the operation config on the router by TELNET/SSH session once it is added from the tool.
This is a feature request that I have already captured.
Sham, I found it unusual that the IP SLA monitor creates sla objects that appear in show output, and actually run, but are not available to edit within the configuration. Odd!
My recommendation for the originanl poster is to create your own SLA Monitor object using cisco.com documentation as an example.
ip sla monitor 100
type echo protocol ipIcmpEcho 192.168.1.100 source-ipaddr 192.168.1.1
enhanced-history interval 300 buckets 50
ip sla monitor schedule 100 life forever start-time now