Did you find a workaround as I am facing exactly the same issue.
You can switch the branch of UncleCheese module to 3.0 and do need to do some minor alterations (method signature need to be matched to the framework's implementations).
When you use a new deployed AWS service, like Frankfurt, you will have the challenge with the V4 authentication. UncleCheese's module does not support V4 at it uses the 'undesigned' PHP SDK.
I could spent some time on upgrading the module and use a more current PHP SDK but you will lose some of the nice visual formfield features.
Now I am looking at re-writing my own FileField with its CMSS3FileAddController but am not sure if I re-invent the wheel right now.
Did you have any success with the S3 UploadField?