jets3t has always served me well and plays nice with S3sync.  http://jets3t.s3.amazonaws.com/index.html for info, https://jets3t.dev.java.net/index.html for the project page.

"To support Europe we enhanced Amazon S3’s API to include a new parameter for locality. The name of the parameter is LocationConstraint, and if you use it then buckets are created in the location you specify. Existing applications will not be affected, and will create buckets in the United States, because that’s the “default” behavior. Pricing is slightly different in Europe; although not but much. Use the AWS Price calculator if you want to estimate what your costs will be."

This comes from the AWS Blog http://aws.typepad.com/aws/2007/11/notes-from-berl.html

I would assume this will require some change to S3Sync to support selecting whether the bucket is created in the US or Europe.

-klp