I've found this... So I guess it won't work :(
Unlike Word, PowerPoint and OneNote 2010 it’s not possible to have
multiple authors working on a document at the same time in Microsoft
Excel 2010. However, if you have access to the Office Web Applications
– where it is possible to edit Word, PowerPoint and Excel documents
via a browser – there is an alternative available.
The Excel Web Application has a feature known as Collaborative Editing
– which is basically the co-authoring offered in Word, PowerPoint and
OneNote – allowing multiple authors to work on a spreadsheet at the
same time. Unlike co-authoring in the client, edits by other users
working on the document are not applied when the document is saved,
rather the document is updated as the changes are made.