I’m going to say something, and you can all think I’m an asshole if you like, but here it is anyway.
Speaking for myself here, I hate introducing girls to my parents. So much so, that I have only ever let them know about one girl, my current girlfriend, and even then, that was only after we decided we would marry. Otherwise, they would not even know she exists to this date.
If I took a girl round to my parents place, and told her specifically not to do something, and she went over my head and did it anyway, I would dump her on the spot instantly, no second chances.
My advice would be to ask him why not, just to know what his reason is. Then, do as he says anyway, even if he is being unreasonable or does not have a good reason.
His parents are his turf. If you go over his head and bring them a gift, it is like if he lets you into his car and asks you to not touch the radio settings, but the first thing you do is change station and crank up the volume anyway.
These are not mutual friends or strangers you met on the street, they are his parents, and honestly, you should be thankful that he is willing to let you speak with them at all.
Whatever you decide to do, keep in mind that some of us are a bit strange concerning parents, and there is little to no chance that you can ever do anything about it.
Ask him why not, then either go and don’t bring a gift, or don’t go at all.