URLs in file's URI field?

Hi. I'm trying to set up migration classes for copying our content from drupal 6 to drupal 7. I'm currently stuck on oembed. As far as I can tell, I need to create a file entity for each inline object. This worked great for files and images. It looks like the file's uri is used to store the url of the embed.

The uri field is unique. I guess it makes sense that if I rick roll someone in one node I'd reuse the file entity the next time i do it. What happens if another user embeds that video though? Do they use the file entity I've already created?

The uri field is also short. We have a couple URLs that exceed the 255 characters allotted.

At any rate, the second problem has convinced me to alter the schema to increase the size for uri. If I do that, I could append &drupaluser=$uid to the url to solve the first problem. What I'd like to know is if there's a more oembed/media friendly approach that I should try instead? It seems unlikely that I'm the first person to take exception to using uri in this way, and google hasn't helped me find any similar issues, so I'm hoping there's something else going on that I'm missing.

Thanks