How can I insert an html block of code below the nav bar on an index page?

I have an HTML code (<script>) that I am trying to put below the nav bar on a single index page. I know traditionally one cannot put code blocks in index pages, but I am hoping there is a work-around - possibly using the footer/injection code or the header injection coding (but somehow getting those to appear underneath the nav bar and not in the footer or header).

Any help on this would be greatly appreciated!!

7.0 I find that if I put a code block in the header of an index page all pages in that index are affected by it which could be good or bad.