You can create your own axis objects as follows. (Lost the source URL / gist for this snippet, so you cannot do justice where it should)
axis = r.g.axis(85,230,310,null,null,4,2,["1", "2", "3", "4"], "|", 0);
axis.text.attr({font:"12px Arial", "font-weight": "regular", "fill": "#333333"});
// y-axis denoted by setting orientation to 1
axis2 = r.g.axis(40,230,300,0,400,10,1);
So, create a regular line graph with two rows, and then draw another axis
Otherwise, configure several axes and then adjust the labels: -
var lines = r.g.linechart(10, 10, 300, 220, [[1, 2, 3, 4, 5, 6, 7],[3.5, 4.5, 5.5, 6.5, 7, 8]], [[12, 32, 23, 15, 17, 27, 22], [10, 20, 30, 25, 15, 28]], {nostroke: false, axis: "1 1 1 1", symbol: "o", smooth: true});
lines.axis[0].text.items[3].attr('text','my label');