I think you've answered your own question with "Tableau is not an ETL tool."...and you are right it is not set up do this kind of thing....however one thing you might try (seeing as you were prepared to manually copy and paste it) is to use the Export Data function. You'll need to build your Table in a tableau sheet (and may take an while to fully render)....but this exports it into a Microsoft Access database, so should be more efficient that the clipboard and not give up the ghost!
Hope that helps.
Wait for some more time after some time it will unfreeze and u will et your data.
Thanks for your responses - we ended up doing actual ETL and not using Tableau for this purpose, which I figured we'd have to do anyway. The data was too big for either of the solutions to work without freezing my computer up!