We use a python script combined with Basemount. The python script takes a BaseSpace project name and an AWS S3 folder as input. Then the Boto3 package is used to connect to AWS, check that the FASTQs are already uploaded in that AWS folder and then uploads them if they aren't.
It's possibly not the fastest way, so if you're doing something like WGS you might want to look for a different solution, but for our application, it works perfectly fine. It could also be further automated to check for new data regularly.