I spoke too soon. The blog indicates how to do it in DTS, but not SSIS. The SSIS object model doesn't seem to provide that information. Am I missing something?

I've managed to answer my own question, with the help of Jaime Thomson:

http://blogs.conchango.com/jamiethomson/archive/2005/02/28/SSIS_3A00_-Dynamic-modification-of-SSIS-packages.aspx

You got me there. My bad.