Several days ago i faced with prestashop problem. I tried to hook right column cms block to header. But as prestashop developers says, that it was developed to hook only left or right side.
So here is my solution for this:
in global.css i changed right_column class position to relative and moved it up.
CSS looks like this after my changes:
position: relative;
left: 0px;
top: -200px;
width: 191px;
margin-left: 21px;
overflow: hidden
After this my center_column looked weird ( not full width ) and chaing it's width changes everything ( right_column drops down and starts to move... ). So i figured out this solution for the place: I changed center_column position to absolute, added padding-left so it dont overlay on left_column and added width which i was required from the beggining.
CSS looks like this after my changes:
position: absolute;
padding-left: 290px;
width: 810px;
margin: 0 0 30px 0;
overflow: hidden
Good luck with you prestashop hacking!