I believe I mis-spoke in my earlier post when I said you need to select "book to occupy my home resort" if you want to pick your Marriott week before you deposit to II.
This has worked for me in the past and then I have called Marriott to excercise the lock-off option and then deposit the separate units to interval. This incurrs a lockoff fee but I have never been charged a cancellation fee as Gaff describes above.
It appears that you can also pick your week to trade if you chose " Owner Deposit" under "Exchange your villa" If you do this you get the same calendar you see when you select "book to occupy" , showing the green highlighted dates for those weeks that are available. Not sure what happens next . I image that you get a confirmation email and then have to call II to actually deposit the week. Does anyone have any words of caution about using this approach? One thing I am unsure of is weather you can book your entire 2B and then call Marriott to excercise the lockoff or if you should just book the master suite first and then go back and book the lockoff unit - sort of doing and automatic lockoff . Dont really know if it works this way though.
Beware as Kathy Pet found out , that if you chose "Marriott Vacation Club Deposit " under "Exchange your Villa"., Marriott gets to pick the week for you, then deposit to II. Good deal for Marriott as they can use excess inventory from a low demand/low trade power week, but a bad deal for us.