No, I'm not suggesting you hitchhike oop north - the British ceased stopping for hitchhikers back in the 70s. I'm proposing you visit the Freewheelers lift-sharing website. It's a rather nifty place for drivers and passsengers to meet, and there are already two lifts on offer to Gleneagles for the big G8 romp. One's going from Newbury, the other's a very cool bloke offering 6 seats leaving from Glastonbury next Wednesday (he's either a local Somerset man or a hardcore Glasto fan). If you're planning on driving, there are several people looking for lifts from all over. It's not only very green, it's also a - potentially - superb way to make some new friends. G8 Gleneagles liftshare page. (thanks, Daniel H)
I actually did manage to hitchhike part of the way there, and hitching became very easy whilst there were lots of activist-driven minibuses driving around Stirling and the rest of Scotland.