I got a GreaseMonkey script, FreeRepublic TreeViewer, that makes a button that pops the posters into a table format, I can copy that into a spreadsheet, select/copy the "poster" column into my word-processor, then search-and-replace the line-breaks with ';' — copy the result to the "To" box, done.
I could make it so that the button would do all the proper formatting, but (1) I'm lazy, (2) I don't really like JavaScript, and (3) having a multi-step process gives me time to abort [where a one-click solution wouldn't].
I have that script. Once, for fun, I ran a report on the first Undead Thread, which had over 65,000 posts. It took it about 10-15 minutes to run.