I used to be OK in Excel but that was ten years ago but if I can remember correctly your hyper-link file must be in the common folder and that only works for Excel sheets (could be wrong though). I am also not sure that Excel will understand the .ai file but it should understand an external link to a server when published to html. This means that your .ai file must be uploaded to the linked sever through your html editor when the web page is published so I would suggest that you have a look there.

I may have mis-interparated your question so please come back if I have please come back. If I haven't do a search in Google on "Hyper linking in Excel through html" or something like that.