I had a similar problem with my T1. Bought the right post, right clamp (a slim lightweight one, very trendy), couldn't tighten it enough. Damn seatpost spun around with little more than a nudge.
So I tried the old G-Sport George favourite and tried making a shim from an aluminium can.
It certainly made the clamp grip, but when I tightened the bolt it seemed to spin forever.
Then the clamp suddenly broke
. Snapped at about 1/3 of the way around from the back.
So, bit of a cautionary tale there.
A more burly clamp was the solution, but it still takes forever to get to a stage where it's really gripping the post, and there's about 5mm of thread showing from the bolt.