...you won't get your hose grabbed... it is more likely that your buddy will get the regulator jammed into his chops.... but that is another issue...you never know the exact moment that your buddy will grab your hose away...
If you read Jonnythan's post (or just think about it while sitting there breathing normally) you have a bit of juice left even after a normal exhalation... and you aren't going to die instantaneously even if you make the extra effort blow it all out just before giving up the regulator. Try it sitting there.... blow it all out and see how long you can last before you have to suck some in. How many seconds did you last before you passed out and they called 911?
Using the long hose you have your backup bungeed right under your chin and if you are the frantic type you can have it ready to cram into your mouth the moment you take your primary out. But folks who are more concerned about their air than their buddy make crappy dive partners. They dangle the long hose out there without looking to see how their buddy is doing whilst they fumble around trying to take care of themselves. I either correct that little issue or we don't dive together again. When Shane and I do the drill I don't even think about putting my backup into my mouth until I am sure he has my primary in his mouth and has it cleared. Shoot I don't have to worry... I've got air sitting right there under my chin for pete sake.
So to answer your question (after an unforgiveably long preamble):
Just breath normally... like you are right now.