Not 100% sure whether this is relevant to what you are doing, but you may be after this.
Virtual hosts (at least, name-based ones) really only work based on the Host: header being reported correctly by the client - it is therefore fairly essential that the client supports HTTP/1.1, as the Host header is not required by HTTP/1.0.
However, whether this will help you kind of depends how complicated the setup of your internal access is - If you are doing everything based on 'localhost' or IP addresses it won't help at all.
Do you have all your seperate sites stored in different directories, or stored in a more complicated way (IP address based, hostname based etc)?
If you are storing everything in directories, you could prefix all your paths in the generated HTML with a variable, and when you move this to production either search/replace to remove all references to this variable from your code, or populate the variable with an empty string.
e.g.
For developing:
$pathprefix = '/MySite1';
print("<img src=\"$pathprefix/path/to/image.jpg\" alt=\"My Image\" />");
For production:
$pathprefix = '';
print("<img src=\"$pathprefix/path/to/image.jpg\" alt=\"My Image\" />");
...or...
print("<img src=\"/path/to/image.jpg\" alt=\"My Image\" />");
