I wound up just hacking a report solution by putting a PrintMe flag on SalesOrderLineItems and setting this flag to True based on what was selected in the grid on the screen. After generating the report, I update the flag back to False again.
I got this idea from another post on the forum (can't find the link at the moment).
I don't like mixing reporting concerns with data like this on the same record, but this particular feature isn't large enough to warrant an entirely different reporting table structure at this time.