MD5 hash your data. The data can be as long as you want. Then store the data as a database record using the MD5 hash as key. The user can then access a URL like this:

index.pl?eJzTz9AvyMku0jfWLy8v1wMx9fKL0vWLiouBHACWdQpk
[download]

...and your script will search for the database record with that key and return the data in its original form.

This was already said above, but I thought I'd explain in more detail.