Is it possible to type something into the address bar without going to the URL?
This is technically impossible to achieve in the current version of iOS.
Though, you may want to try this trick which isn't right what you'd like to do, but may be a way around:

Tap the address bar and type whatever you want to search
Copy what you've just typed
Tap on cancel in order to get back to your current open webpage
When you're done and you want to search what you typed before, simply long press the address bar and tap on Paste and Search.


As I said before, this is not what you'd like to do, which indeed is not possible to achieve at the moment. Although, this may be an easy and quick trick as a way around of what you wanted to do.
Hope this helped you out!