Can I use a seat-post clamp/collar on the seat-post itself to prevent slipping?
You would be best served by first going to you dealer for advise. I am unsure why you would change the seatpost, as this may provide more salient information regarding your problem.

That said, if you really want to use the seatpost mentioned, it sounds undersized. You can buy seatpost specific shims. I again would recommend going to a LBS as they have the ability to best gauge the correct size shim, and order it for you. CF frames do not handle stresses that they weren't designed for well.