You can, but there are some issues with this method:

1. You will need to attach the support boards to the SIDE of the 4"x4"s with two 1/2" galv. lag bolts.
2. The 4"x4" posts are not always located in the best position for the handrail. And, the desired locations for the handrail posts are not always in the necessary location of the 4"x4" post.

It is easier to build the deck first. Then attach the handrail posts to the frame of the deck.

A good example of placing the posts on the inside of the frame, but not extending to the blocks, can be seen on the Wangsness Deck Project.