How I added the breadcrumb JavaScript to the bottom of the page in a Sandvox created site.
You need Sandvox Pro to do this. This is experimental and not intended to be done by Sandvox. If you want to 'play it safe', read no further.
1. I downloaded the breadcrumb javascript from this site:
[http://mindpalette.com/tutorials/breadcrumbs_JS/index.php]
2. I unzipped the download and customised the script as explained on the above linked page and in the unzipped script file.
3. I renamed the edited script breadcrumb.js for ease of understanding. You can rename it or not but be consistent with the name where it is needed.
4. I copied the sample code for placing the script:
<script type="text/javascript" src="MPBackLinks.js"></script>
and edited it to the name and place where I placed the script, (I also added a font size adjustment):
<script type="text/javascript" src="http://www.isawhow.com/javascript/breadcrumb.js"></script>
5. NOTE: To edit the Heading or Sub-Heading field you must have the Home page selected in the Site Outline on the left in Sandvox.
For ease of placement in my whole site, I pasted the script in the Sub-Heading of the Title bar by clicking in the Sub-Heading and choosing to Edit Raw HTML...

Nothing appears until the site is published.
6. Sandvox warns the that this area should not contain 'scripting constructs'. I continue because I don't know what that means. Wimps may cancel at this stage.
How to upload the Javascript using Sandvox:
7. In Sandvox: I added a Download List Collection, titled: javascript and hide it from the collection index and site maps by unchecking those options in the Inspector.

8. I added a File Download Page within the 'javascript' collection and Choose... breadcrumb.js as the file download.
9. Rename in the Inspector, the Title to breadcrumb and checked that the File Name is breadcrumb

10. I published the site.
Below is the Breadcrumb bar placed between horizontal lines on a single page:
