Dolphinhead,
I was researching the whales in the Silver Bank and there are a couple of operator out of Puerto Plata that do "soft in encounters" where you are on a liveaboard and they transport you to an active whale are and you slide into the water with your group and basically float in a big group with your snorkel gear. You can google it but these liveaboard trips (7 days) cost around $3000 per person for the week. I haven't found any day trips for the soft in encounters, but who knows?
k.