In the Local Publishing Administration Guide, you'll find this documentation:
The postexecution phase provides for two types of declarations: <programs> and <services> to identify programs to be executed and services to be stopped or started. The attributes for the <program> and <service> elements of the postexecution phase include all of the attributes defined for these elements in the preexecution phase. Additionally, the <program> element of the postexecution phase provides four additional attributes: path, pathtype, regpath, and regvalue to specify the execution of a program file contained elsewhere in the filesystem. The pathtype attribute can have one of two values: "simplepath" where the path attribute specifies a complete pathname, with or without the use of environment variables; and regprependpath, which makes use of the regpath and regvalue to identify the location of the program executable.
So, the appropriate syntax for your example would be:
<program type="exe" typeaction="runandwait" name="ssvagent.exe" pathtype="simplepath" path="%programfiles%\Java\jre\bin" successcode="0" failureaction="stop" enabled="true">
-high -jpisetup -old
Thank you Lawrence - I knew it was probably an RTFM kind of deal :-)