Are you sure there are no drivers? TIM doesn't make their own "chiavette" they rebrand existing ones. It seems they have two versions, Huawei E353 and Olivetti Olicard 145. Both should work on OSX.
This is a link for the Olicard driver which I got off the Internet for you but am not sure of the contents. Google your drivers first.
If your friend speaks Italian, then this forum could be of use.