please look at the outline of the planed DIV frameset of Moodle. Could you use the "wrapper" DIV for overlib, which is planed to surround the whole page?
get to know somebody who knows where in the Moodle code DIVs can be placed best . At the moment the DIVs "wrapper", "header", "nav-bar" "containerContent" and "footer" are planed to be written in "header.html" and "footer.html". Can you propose a better place?