Inhibitor, let me applaud you for your generosity towards us internationals. It's not something you see every day and it's much appreciated here.
Now not to sound negative, but sadly I feel that this idea won't work. Mattel is NOT overcharging international fans for shipping. What they charge is what it actually costs and there are no cheaper methods other than what they offer (Well, there are a few but they are so unreliable that if one gets his stuff, he might call it a very very lucky day).
So in the end the international fan would have to pay not only the exact same cost of shipping, but also domestic shipping (from Mattel to you) and Paypal fees.
Sure if you ship everything together in December that would be a different story but still the costs saved would be really very little. I would estimate the costs for 17 figures to be about $150-$180 (I bought like a thousand toys of all sizes from US so I always have quite a good idea of the actual costs). That's like saving $70 but still with shipping from Mattel to you the international fan would have to pay at least another $120, so again it will be more expensive for them than buying directly from Mattel.
Once more, it's very nice of yours to offer to do this, but the hard truth is it will not work.