I usually try and get them to hear the potential excitement by trying to describe it... for example -
"...yeah - that's not bad, but ya know what would really make this jump out? An acoustic guitar... can't you hear it starting quietly, and then building in dynamics and hearing the attack of the strings as you play it harder for the chorus? And then you back away again for the verse... and you get this nice build/slowdown effect that will really capture your expression... it would really "sound!"
By this time, if I've described it well-enough, their own creativity kicks in and they see what I'm getting at and they get excited about the possibility, OR they've got their head up their arse and they flat-out reject it (at which point there's nothing you can do -- but thankfully that hasn't happened too often!)...
The other thing I find I say often is "...listen -- it's completely your decision, but honestly - that part doesn't have the impact I think it could have, what about if you did ___ , etc......"
Both these approaches usually get the client to think about it and reconsider...