[ehsizzup]

Is there a way to mod or customize SP so that we can place blocks in more places?

Specifically, side blocks should be able to be placed in rows within the the top block section.

[asude]

This isn't a built-in feature. However, SPortalBlocks template is very simple and flexible. You could modify it as you like. For using two block types in a single row, you can see this post:

http://simpleportal.net/index.php?topic=2460.msg16288#msg16288

You can even remove styling from the actual block and display blocks using template_block() template with PHP block, more than one in the same row.