[MC5C]

In classical guitar much depends on what came before and what comes after. Sometimes a finger needs to be in a certain place because it needs to play that same note, or one nearby, in the next beat or two. That fingering of the good old G chord is indeed a stretch for the fingers, particularly on a classical width fretboard. You could see if first finger on the B (fifth string second fret) and second finger on the low G is easier and more workable. But you may equally find that Mr Noad has something in mind for the first finger that makes his fingering important. Without seeing the notation for the piece, that's all I got...

Edit:Just saw this: "The measure plays 1st and 5th string together, then 6th string and then 5th string." I would, if that was all I had, play that with second finger on the B (fifth string) and fourth finger on the high G, and play that two note chord, keeping in mind that at that point you don't need to have your finger on the low G) and then (presuming the high G doesn't need to sustain) take my fourth finger off that high G, let it mute out, and play the next two notes with my third and second fingers. It all depends on how long each note needs to ring out for