Alright I finally got it. Yeah, a 3156 and a 3057 should fit into the same socket like you said, but for the life of me I could not get it to snap in there. However, what I did instead was bend the little metal contacts on the base of the bulb so that there was only one contact on each side of the bulb. (just like a 3156 single filament bulb) Thanks everyone for your help. I knew it would be simple, I was just a little confused. Here is the result:
confused on the bulbs. should i get the 3156 or a 3057 bulb or could just a stock bulb work and just tape off one of the leads like the OP says or somewhere in the thread i think someone just taped off and it still fit in the socket!?