The fixed element doesn't exist in the normal flow of the document so the only way for other elements to account for it is to use padding/ margin/ or positioning in various guises to keep clear of the fixed element.
You could use relative positioning on the container that follows the fixed header using an em height for the value "top" equal to the height of the fixed header. Or as you mentioned earlier margins or padding would do similar also. (Or even absolutely place the whole layout below the header.)
There is no other choice but I guess this begs the question "why do you need to find another way"?