Yes, you can walk from the front of Epcot to YC/BC and Cape May Cafe, as the PP noted. This will require that you have a ticket to use for entry to Epcot, however, as you actually have to go through the park and exit at the International Gateway. If you have a hopper that's been used that day, an AP or and MYW base ticket that was used that day at Epcot, you're fine. If you have a MYW base ticket that wasn't used that day at Epcot, however, you won't be able to enter Epcot if you've been to another park that day and if you haven't been to a park you'd have to burn an entire day just to go through Epcot.
If admission to the Epcot isn't an issue, then this is a viable way to get to YC/BC from the Poly. As noted, however, it is a fairly long walk through the park. If admission to Epcot is an issue or the walk isn't an attractive option, boat or monorail to the MK and bus from there to YC/BC, or bus to DHS and boat from there to YC/BC are the two best alternatives using Disney transport.
All of these routes are workable for your return trip after dinner provided that the park being used as a transfer point is still open. If non of those three parks are open, however, you will need to take a bus from YC/BC to DTD and transfer to a bus back to the Poly.
