Not all servers are set up this way, but many are.You could use:
http://11.22.33.44/~example
"example" is not going to really work - you'll have to know the particular weirdness of the server in question. WHM servers, for example, create the username by using the first 8 letters of a domain (although this can be changed). Therefore, example.com's home directory on a WHM server would look something like:
http://11.22.33.44/~examplec
The name is how Apache figures out what domain so serve up. Trying to bypass it as you are is likely going to be problematic in many cases.