Auto-populate fields using GET

I’m just doing a project now that makes very heavy use of the custom field types and adding new items that are specific to certain values in the fields. To make it easy for the users I want to have links to the admin panel to add a new post type but certain custom-fields are pre-populated by the query string (a la GET).

What would be cool is to have a feature in wordpress where if you have certain query strings that if they match the custom field keys it will pre-populate those fields with the values of the query string.

May not the most widely requested feature but something that would be amazingly handly if it could be done!

(BTW, if anybody knows a plugin where this could be done, let me know! Thanks.)