I've been trying to resolve the same problem, in the end the solution I went for was to create a bookmarklet so that I can click once and have the details entered into the fields without having to look them up. This does of course present security implications depending on how you safe you consider bookmarks in your browser! But for me it works well, here's the code I used for the login page on my Plesk 9.5.4 install:
The login page actually uses frames, took me a while to notice and then get the bookmarklet working! This code works for me using Safari 5 on Mac OSX 10.6.7.