Platinum package can absolutely be booked online. It can only be booked at Deluxe level resorts - no exceptions.
It is EXPENSIVE. I priced a 7 night vacation for two at the Grand Floridian with 'MYW+Dining' package with Park Hopping and WaterPark Fun & More. that came out to around 5379$.
The SAME package on the Platinum Plan which includes unlimited recreation (golf, water vehicles etc), unlimited tours (like Keys to the Kingdom, Segway Tour at Epcot etc) and table service for all three meals each day and a free snack per person / per day, 40 hours of childcare a week, VIP Fantasmic! seating and free Cirque Du Soliel tickets.
You'd better make plenty of use of all those included items and love it to death tho.. it adds about $265+ per person per day OVER the MYW+Dining package quoted above. Grand total cost for the same package above on the platinum plan for 7 nights : $9112.
Knox