You could try to push it to become possibility, I would have similar needs later in spring and burger would be definitely something that would sink down easily
It just can not be impossible to arrange a preorder food in J, regardless of the planned class of service as we know now they come from the same place. Naturally it could be that there is some type of internal sales ongoing and food included in the fare is in the different bucket than preorder and units compete against each other on how to get most customers reject the included dishes but go for the extra pre-orders and hence Y-preordered free-of-charge to J would mean loss for the other unit.