Accessing ELGG in a subdirectory, FROM the domain root directory?

I know this has to be simple, but I'm pulling my hair out trying to find a simple answer.

Example:  elgg is installed in

     I want to type "" in my browser and see the elgg index page come up.

In the file, I added the "RewriteBase /subdirectory/", so it is installed fine.  My site is on a Linux server with  What is the easiest/best way to do this?