For Now i could not find a way to use system Paper Sizes but did find a way to add new paper sizes to the jsPrintSetup.getPaperSizeList()
jsPrintSetup.definePaperSize(101, 101, "Custom", "Custom_Paper", "Custom PAPER", 250, 400,
jsPrintSetup.kPaperSizeMillimeters);
jsPrintSetup.setPaperSizeData(101);
According to the Documentation
void definePaperSize(in short jspid, in short pd, in wstring pn, in wstring pwg, in wstring name, in double w, in double h, in short m);