Hello AE,
First and foremost, it all depends on where you have your parties. I know I have been to several parties where the place just wrapped them up in a garbage bag and gave it to the birthday child at the end of the event. I, myself find that quite rude as well, however it is their b-day party and they can do it anyway they like.
On the 4th parties that I have had for my son, I allow time for him to open his presents. I think this teaches them how to be thankful and say "thank you" to his friends at the time they presents are given. IF your family is giving him "outlandish" gifts, then you should limit those to be opened at the party and give the birthday child the bigger presents later on their actual b-day or designate another time. I don't take any presents except maybe 1 or 2 to his parties except for the folks who actually attend. It does drag on and on and as you know kids attentions span is only so long.
So, just take a few of the gifts, say if your Mother buys 3 gifts for your child, just take 1 of them and then have a smaller celebration at another time and let them open those gifts later. Not only is that better, but it doesn't make others feel bad if their gifts is not comparable to a more grand gift. Plus, it doesn't make your child look greedy.
Both of my son's grandparents live far away, so we don't even take those with us, we leave those at home to open on his actual b-day date!
Good Luck!
G. B.