Custome Downloadable Product

Hi,
Need help on one issue we are facing :
We want to use a downloadable product (ie digital product) but along with the product file we also want to take an input from users on Product details page. For this we can create the TextArea or Upload File options on product detail page. Now the final output which users can download will not be the file which was uploaded for Product by admin but a custom file depending on the user inputs provided on Product Details page and this will vary for each customer. On order submission the the custom product file will be created offline and uploaded back to My Order page from where the user can download it.How can we achieve this using Magento?
Thanks in advance,
Amit