Sorry for the delay in responding to your post. First, I do want to warn you this is not something we officially support. By looking at the code this should work but you will need to try it. The code you will want to use is:
EJEJC_show(URL, 'i', false);
The URL above is the URL you want to appear in the light box. It cannot point to an image, it must point to an actual web page.