I definitely would spend the most time using Marc's first suggestion, by choosing a target note (for example, a D#note, 4th fret of the B string) -- play it, and then grab the 6th fret of the G string and bend up to it so both pitches are in tune. (This would be a full step bend -- going from a C# to a D#).
Do this repeatedly to start to feel how much to bend the G string up so that it is in tune with the actual target note.
The bend that happens in the solo of Amarillo is in this same spot, but it is harder to hear whether you are in tune, because you are playing an F# note at the 7th fret of the B string with it (instead of the same note at the 4th fret).
So try this similar exercise- play the 8th fret of the G string with the 7th fret of the B string. Study the sound of those 2 notes -- now try the bending lick again and when you bend up, try to get to the same "in tune" sound that you just heard by picking those 2 notes at the same time.
Practice these little exercises often, and eventually you will get more and more familiar with the sound you are going for, and the amount of force you'll need to bend the note on the G string to get it in tune.
Hope this helps ... be sure to let me know how it goes!!
GT Guitar Coach