While I think he will be on the block at times, I think his biggest value will be playing a similar role to Garnett in the offense. This means playing a lot on the high post, running pick and rolls, and also helping to initiate the offense.
What I think could be very interesting for the second unit could be if they sign a guy like Hill, and resign Davis, you could see a lot of a unit of House, Hill, Walker, Davis, Sheed. And in that group, I think you would have Hill running the point, with Wallace playing in the high post, Davis sitting on the weakside paint, and Walker as your main low-post option. I think you would see the same thing with Pierce.
This was tough to do when KG was hurt, because defenders just were not sticking to the C's big men enough on the perimeter, but with both Wallace and KG, it makes them much more dangerous, and open things up for the C's SF's to hit the post.