I bought a torx opening off EBAY in the past, the exact same style as you see in this auction:

http://cgi.ebay.com/Apple-Mac-128k-Case-Tool-Opener-Torx-T15-Screwdriver-/170586354424?pt=LH_DefaultDomain_2&hash=item27b7bd32f8#ht_1146wt_1141

But in my younger days, when I owned a Mac 128k in 1984, I filed down one of my father's 15" flat-head screw drivers and used that to open the case. If you use enough pressure it will work fine without stripping the torx screws.