Chrom Octave Shake

6th chorus So Blue For You, bar 8 - mouth dry, chrom covers sticking to my lips so its hard to get the shake. I tried a lighter contact on the harp to see if that would help but then the tongue cover doesn't give me a true octave shake. When I try it on its own (out of context) and lick my lips first, it seems to work OK but back in context and by the time I get to that bar, I'm dry. (come to think of it, that's why we go into bars;-))

So is there any 'tip' or is this another case of "keep at it and it will come eventually"??