I have knocked up a quick piece of javascript that can be injected into a page and added to a bookmark that uses the site: search as Erel posted in another thread. It is very basic and I have only tested it on Google Chrome.
Copy and paste the code into a bookmark, call it something like Search B4PPC.
It doesn't run from all pages, presumably something to do with javascript injection or popup permissions.
I am a novice at javascript, someone else may be able to improve it.
javascript:var search=prompt("Enter B4PPC Search");if(search != null){window.open("http://google.com?output=search&q=site:basic4ppc.com%2Fforum%2Fquestions-windows-mobile "+search+"\n","_Self");return false};
Click the bookmark and you should see a pop up prompt, enter the required search terms, a google search page will then be displayed, you will then need to press return to run the search.
It's not a perfect solution, but it may help for now.