"However, i was told by someone else that they did it by just pouring the cleaner slowly into the vacuum ports (with a funnel obviously). Would this be the same? It seems easier to do it that way."
It will stall and you will "get a loud bang"

if you pour in too much
"I just bought the B-12 Cleaner today and was going to do it this week but i just remembered that i JUST changed my oil less than 500 miles ago... So does that mean that i shouldnt do this untill i need another oil change?"
If is up to you but a lot of crud will get to the oil.
Read the post by Ike three weeks ago. "What did I do wrong here" in this forum. Good luck.