No extension do it, that I could find. I tried for you 😉 Now, I could have missed something, so you can look too. And even it's not currently available, it could be done in the future with an extension. Post your wish for that meta-search in the Opera Add-on forum, to let developers know what people want.
For the moment, if you want to do a meta-search, just go to the website of the search in question, right click on the search bar, to add the search engine to Opera, and note the letter of the relevant code to type before the search query. Then just type the code letter(s) [space] before the search query. With one letter, you can most often get a search of three or four engines in one shot. That's still -- in my book -- a pretty good bargain.
