Buggy board is the best plan. Even if LO does sit in it it won't be for long and will be a waste of money to buy double buggy. I'd use a buggy board, perhaps if you pick up a cheap double stroller second hand and just use it if you are going out for a long trip? If you are trying to wean him off I wouldn't bother tho, if you have it he will sit in it so no seat, no option!