Brian, it's a bit expensive for a one off job, but this, "Veritas Metal Bender & Axminster Power Nibbler - PACKAGE DEAL £48.35". Axi, sorry, I lost the link, just search "sheet metal nibbler. This definitely WILL do the job in 2mm ali.
I have one that looks exactly the same (but I bought mine off a market stall!) and although "officially rated" for sheet steel up to 1.8 mm thick, it actually does 2 mm, no sweat, and I promise you, with NO distortion.
I've done it several times, including on aircraft sheet metal skin. It's driven by a normal electric drill, and the only downsides are A) VERY loud noise (the sheet acts like a sounding board), and B) "millions" of tiny, very sharp crescent-shaped off-cuts all over the floor, which WILL stick in your shoe soles (he says ruefully).
The other methods (above) will work but will need quite a lot of work.
And sorry gents, it's just nonsense to say a power nibbler won't work on 2 mm ali. Mine certainly will, as above, and mine's nothing special - it's certainly not Veritas and didn't cost 50 quid!
If you want I can put mine in the post and you should have it in a week or so. I'm in no need of it right now. PM me 'cos I've probably lost your address - and I've got a few other things on right now too (NO, sorry, it's still NOT "your" aeroplane!).
AES