I have had to give Baytril orally. There are a few ways that I have done it, but it all depends on your cham and his/her demeanor. If they instinctively gape at you when you get near it, just squirt it in (although be sure not to squirt it so hard that it goes down its throat). I have also grabbed the cham from behind like you said, but also you can tap them (gently) on the nose and they will (most times) instictively gape at you.
Another way to try is to inject the liquid into a juicy feeder worm, such as a horn worm, butter worm or silk worm, and give them the worm. Kills 2 birds with one stone that way.