something like 240grit sandpaper to get the scratch out, and work your way to finer ones (over 1000, potentially) until you're happy with the finish. You'll lose the oxidisation to start with (and that might take some work to get off before you actually get to work on the aluminium itself), so will look different, but it will come back.
I'd give it a go if the alternative is buying a replacement part (nothing to lose), though for me I'd probably just live with the scratch.