Well you've already noticed the difference in measurement standards. Its anoying to say the least.

If the Easton seatpost doesn't work out then as daneil linked to you can get Truvativ single clamp seatposts that will have the desired setback. They are available in 27.2 mm and they come in the XR model as pictured and a TEAM model is also available that's a little lighter.

Regards, Anthony