American credit card, Japanese VPN (had a site I used) and some tutorial on how to do it all. You can buy the games just fine with an american credit card, though Visa Debits gave me issues. If you have a Master Card, you should be good.
You can try using this to reduce the size of the gif (resize, reduce colors, or cut frames), but yeah getting any kind of complex gif will be a challenge. Before my Sonic avatar I tried to use a really short Legend of Zelda gif but it didn't work out.
As for Gackt, he was staff for awhile, maybe they have higher limits. Another possibility is a higher-up could have set it for him, from my experience they can bypass the limits. I don't recommend trying this yourself though xP
Gotta tell ya, frustrating man. Can't seem to find an image that fits with these size requirements, even as a subscriber still an issue .__. I want a good Dr. Evil GIF that will actually work on this site, I know I've seen fancier animated GIF's than just changing colors and a spinning icon (Gackt used it awhile I think, from Ghost In The Shell).
I figure I'd ask you, since you have an animated avatar x_x; how do you get them to work here on X360A? Every time I've tried to use a GIF, it simply freezes the image and uses whatever frame it froze on as the picture.
I saw in your sig where you are seeking some Viral achievements, for me personally I'm after the GTAIV and Banjo-Kazooie ones if I manage to get the BK one, I can trade that one off to you for the GTAIV one.