Assuming that you are in SVN, splitting your week is conceivable but not easy. You can book full weeks at your home resort at 8-12 months out. You can book full weeks at other SVN resorts from 3-8 months out. Stays less than 7 consecutive days, including your home resort, can only be booked at 3 months out.
So, yes it can be done, but it comes with a bit of a risk.
From MSC:
Starwood Vacation Network Float Period
When confirming reservations eight (8) months to three (3) months prior to your desired arrival date, you can reserve:
Seven (7) consecutive nights or more
Beginning or ending on an established check-in day
In any season
In any villa type
Starwood Vacation Network Options Period
When confirming reservations three (3) months or less prior to your desired arrival date, you can reserve:
Nightly stays or more
Beginning or ending any day of the week
In any season
In any villa type
Borrow StarOptions from your next Use Year