Delaying an action until a file is downloaded

Hi All
Looked and looked but can't find a solution.
Essentially, I want to move a file somewhere after it is completely downloaded.
If I create a rule to move say a dmg file or a music file from the download folder, that is fine if already downloaded. Some files will have the proper extension as it is being downloaded (not *.dmg.download if downloaded via safari) and Hazel tries to move that file over and over with an error!
So - how can you get Hazel to WAIT until it is completely downloaded?
Thanks
Andrew
Looked and looked but can't find a solution.
Essentially, I want to move a file somewhere after it is completely downloaded.
If I create a rule to move say a dmg file or a music file from the download folder, that is fine if already downloaded. Some files will have the proper extension as it is being downloaded (not *.dmg.download if downloaded via safari) and Hazel tries to move that file over and over with an error!
So - how can you get Hazel to WAIT until it is completely downloaded?
Thanks
Andrew