You'd better disable attachments and create one file gallery then, set that gallery with permissions so that anonymous can see (download) files, and registered upload. And use that icon that lindon suggested, or a new one you can use instead. File galleries allow using images in them, but don't force to use images, so that you can use any type of file.
And you can customize the wiki code inserted in the wiki page from that file gallery, with code to show a link to a file, not a thunbnail from an image.
Glad to see other scientists using Tiki (it's a powerfull with lots of potential also for its usage in sicentific fields).
If your scientists are from experimental sciences, you/they might be interested in using Tiki with R together:
Cheers and welcome to Tiki Community!