As an FYI, a properly seated regular ear plug that is designed to block out as much noise as possible is going to be just as effective as a custom ear plug. There is a physical limit to how much noise ear plugs can block as noise is transferred to the ear canal through your bones. That said, it should block plenty of noise. There's just not going to be a huge advantage to going to something custom from a noise level standpoint. If anything, it may be more comfortable and perhaps easier to seat.
I've mentioned this before once, but my friend also took his helmet into Shoei and they took a bunch of measurements of his head and put together a custom configuration of pads which provided a really nice fit. A side effect he got out of this was significantly reduced noise as the helmet pads are snugged up to his head blocking airflow from under the helmet to his ears. He still uses earplugs, but he went from struggling to hear my voice on his Sena to being able to hear me clearly now.