You have a few options but they all involve a lot of time:
1. Take DTD bus from POR & take Dolphin bus back
2. Take bus from POR to any park & take Dolphin bus back
3. Take bus to EPCOT ( must be prepared to use an admission ticket) from POR, walk thru park & exit through international gateway & either walk to Dolphin or take boat to Dolphin
4. Or best idea, just take cab & save yourself some time. Probably would only be $20.
It's hard to say in the morning because the buses from the parks do not run as frequent. But if you are eating at the Poly, I'd take the boat or monorail over to the MK and then take the bus over to the Dolphin.
There are car rental places in DTD area that pick you up, the POR is close to DTD, you might consider getting a rental from one of the hotels there.
Breakfast choices in EPCOT area: Cape May character breakfast at BC, Captains Grille at YC, Kouzinas at Boardwalk, Akershus character buffet @ EPCOT, not really sure what's at Swan/Dolphin. What else?