You should add a custom feature in order to allow people to select different search engine options.
I suck in jquery/javascript. As I said I tried to some customization features but I failed up to the point where I had to do a full rollback (for that I needed to replace multiple parts of the html and css that forgeted everything up, and ending up to another spot where everything IS forgeted up).
I searched on Google like, 2 hours, literally, about how to change background dynamically just by pressing some buttons. I found over 10 scripts and tried to implement them, with no success.
That reminds me, about your concern; Demian suggested me to add text on the search bars with the search engine, very transparent, and when you click the search bar the respective text on it is gone. But then once again I might get in more hassle with jquery and javascript, which I am trying not to do. Also that would mean that if you click the search box again even if you typed your own content, it would be erased (I think). So that's even more impractical.
Also I am disappointed on how laggy the main homepage ended up being in the end.