I am not sure what you mean when you say you want to program in the serpentine stitch. I have the Janome MC6600 P and in order to use the special stitches all you need to do is first put on the appropriate foot, which in your case would be the wide opening so the needle will not hit the foot. Then next you find out by which mode has your stitch.
ie: Mode 2, stitch 26, then decide how wide and long you want then start sewing. If you want your machine to remember what you did, then press the memory key.
Does this make sense?
When I do fancy stitches I cannot use my walking foot, it pulls it weird so the stitches are not always the same.