Try this. It might not be the most efficient route but does work based on quick testing. It assumes that the workbook/worksheet you want to plot is the active one.
string strWBName$ = page.name$; // Workbook name
string strWSName$ = wks.name$; // Worksheet name
int numCols = wks.ncols; // Number of columns in active worksheet
for (int ii = 2; ii <= numCols; ii++)
{
// Specify full range to worksheet columns
plotxy iy:=[%(strWBName$)]"%(strWSName$)"!(1,$(ii))[378:632] plot:=200 ogl:=[<new>];
}