Illustrator JPEGExportOptions Object properties are missing in Object Model

Why don't you use action with Javascript like below?

function exportJPG(pth){ //Export 300dpi CMYK jpg
  var str = "";
  for (var i=0;i<pth.length;i++) str += u16to8(pth.charCodeAt(i));
  var act = "/version 3/name [ 4 73657431]/isOpen 1"
  + "/actionCount 1/action-1 {/name [ 4 61637431]/keyIndex 0/colorIndex 0/isOpen 1/eventCount 1"
  + "/event-1 {/useRulersIn1stQuadrant 0/internalName (adobe_exportDocument)"
  + "/isOpen 0/isOn 1/hasDialog 1/showDialog 0/parameterCount 7"
  + "/parameter-1 {/key 1885434477/showInPalette 0/type (raw)"
  + "/value < 100 0a00000001000000030000000100000000002c01020000000000000001000000"
  + "69006d006100670065006d006100700000000000000000000000000000000000"
  + "0000000000000000000000000000000000000000000000000000000000000000"
  + "00000100>/size 100}" //Probably, parameter for exporter plugin
  + "/parameter-2 {/key 1851878757/showInPalette 4294967295"
  + "/type (ustring)/value [ " + str.length/2 + " " + str + "]}"
  + "/parameter-3 {/key 1718775156/showInPalette 4294967295"
  + "/type (ustring)/value [ 16 4a5045472066696c6520666f726d6174]}" // JPEG file format
  + "/parameter-4 {/key 1702392942/showInPalette 4294967295"
  + "/type (ustring)/value [ 12 6a70672c6a70652c6a706567]}" //jpg,jpe,jpeg
  + "/parameter-5 {/key 1936548194/showInPalette 4294967295/type (boolean)/value 0}"
  + "/parameter-6 {/key 1935764588/showInPalette 4294967295/type (boolean)/value 1}"
  + "/parameter-7 {/key 1936875886/showInPalette 4294967295/type (ustring)/value [ 0]}}}";
  var tmp = File(Folder.desktop + "/set1.aia");  
  tmp.open('w');  
  tmp.write(act); 
  tmp.close();
  app.loadAction(tmp); 
  app.doScript("act1", "set1", false);  
  app.unloadAction("set1","");
  tmp.remove();
  }
function u16to8(cd) {
  var out =
  (cd < 0x80
  ? toHex2(cd)
  : (cd < 0x800
  ? toHex2(cd >> 6 & 0x1f | 0xc0)
  : toHex2(cd >> 12 | 0xe0) +
  toHex2(cd >> 6 & 0x3f | 0x80)
  ) + toHex2(cd & 0x3f | 0x80)
  );
  return out;
  }
function toHex2(num) {
  var out = '0' + num.toString(16);
  return out.slice(-2);
}
var pth = Folder.selectDialog("target Folder?").fsName + "/test.jpg";
exportJPG(pth);