S3 Bucket Notifications on Multiple Criteria

I am running a continuous code deployment with Jenkins that will automatically compile and upload binaries to S3 in parallel for multiple targets.

The final step in my deployment mechanism is to detect that all the binaries for a particular build has been uploaded, and then deploy them together.

S3 has event notifications that can trigger when objects have been pushed, but do they have anything more sophisticated that can trigger when multiple objects have been pushed?

Example:

1. Build machine on Windows uploads binary to S3.
2. Build machine on OS X uploads binary to S3.
3. S3 detects that both binaries are now uploaded and triggers an event.
4. Build machine takes both binaries and releases them together.

Right now the only solution I can think of is to set up AWS Lambda and have the event handler manually check for the existence of the other binary, which may not even be feasible if S3 has special race conditions.

Any ideas?