I would also stay at BC the last night - and since it's soooo much cheaper to add a day to the tickets you already have to buy, I'd do that too so I'd have tickets for my BC stay.
In other words, if I was you I'd book the 3 day free dining package at POP, but instead of buying 3 day tickets I'd buy
4 day tickets at that time.
Then I'd book another separate reservation for the 4th day at the BC.
I'd try and plan to save some DDP credits from the POP stay to use for my BC day. Since the DDP doesn't expire until midnight of the day you check out of POP (which is the same day you check into BC) you'd have until midnight of the day you're at the BC to use any remaining/leftover DDP credits.
Then I'd use the 4th day park ticket the day I was at the BC, and it would be just like having an extra day on the package = tickets & meals!
I know you said you wanted to relax around the BC, but for the small difference in the price when adding a day at the time of the buying the package, it would be so worth it to be able to run over if I wanted to (and of course I would want to - just ask my DH!)
Here's an example pricing at POFQ (I realize you want POP, but POP doesn't show availability right now for my example dates so I just used POFQ because that's what came up first. I really just want to show you how much cheaper it is to add a day to the tickets instead of going without):
8/28-8/31
Disney's Port Orleans Resort - French Quarter
Check In August 28, 2007 Check Out August 31, 2007
Staying for 3 nights, 4 days
Adults 2 Children 1
Room Type Water View
Tickets 3 Day Magic Your Way Base Ticket
Package Magic Your Way Package Plus Dining Package includes 2007 Package Inclusions
Special Rate September Magic Your Way Package plus Dining
Grand Total $1,122.81
Change it to 4 day base tickets and it's only=
Grand Total $1152.63
That's only a difference of $29.82 total (NOT per person, but for 3) to get the 4 day base tickets instead of the 3 day.
Then you could use the ticket's 4th day for your stay at the BC. For another day at WDW, that's a bargain
(You could also add park hoppers,etc. to those tickets instead of going with the base tickets - I just used those as an example.)
I hope this all makes sense to you! Just what I think I would do in your case to get the most out of splitting your stay!