Hey there,
Basicly what you do is get yourself http://www.wowhead.com/?item=29370.
And just use it before using ice barrier, it will make your ice barrier absorb more damage.
I have tested this with a couple of other trinkets, but it only seems to work with Icon of the Silver Crescent.
And how I found this, was by a mistake when i was pvping on my mage, and i popped the trinket and casted a few frostbolts, and the ice barrier after that.
Later when i tried to rebuff Ice Barrier while the old one was still up, it said "A more powerful spell is already active".
-Perz