Well, I just figured it out. If you set your own max and min values for the range, it will scale the data.
So this can be resolved by setting the axis range to 'actual' values:
//chart.googleapis.com/chart
?chxr=0,0,40
&chxs=0,676767,11.5,0,l,676767
&chxt=y
&chs=300x225
&cht=lc
&chco=3D7930
&chd=s:Xhiugtqi
&chg=14.3,-1,1,1
&chls=2,4,0
&chm=B,C5D4B5BB,0,0,0
&chds=a