SIPped, the Polycom fork of SIPp (https://github.com/SIPp/polycom-sipped) has support for including XML scenario files within other XML scenario files through the xi:include directive. It would be good to get this merged into the main SIPp code.

It looks as though the relevant commits are a5011a6, 89b5049, 54866d2, edf7110, 42a425d, a22a738, 3ac1f7f, 97e4d13 and 7463bac.