There is one workaround that you can do that makes this achievable, however your community might get a little confused on how to download the actual file..
If you would like for it to appear under downloads, you will have to first upload a "dummy file" so it appears on the page. (maybe you can get rid of the download later, I'm not sure.)
After that, you can just make a hyperlink to the download location within the download details.
For example, on this download of mine, I have created an image that links to the full size kit download. whereas the actual download button itself only downloads half the kit. due to the one of many constraints of being an iClan customer.
Hope this helps.