How to use placeholder page during site development

Hello, I’ve just purchased a subscription to WPMU and I’m now working on my site. I had a manual placeholder index.html page in place, using DirectoryIndex in the .htaccess file.

However, with this set-up when I go to visit site I end up on the placeholder.

Is there a plug-in or simple instructions on how to keep the placeholder page in place while working on site development?

I tried the Holder Theme but it does not allow the display of a simple, blank page with a single graphic in it.

Thank you for your kind assistance.