It's better to stick within the conventions of "boxes" being the content containers in the side columns. Take the advice of people posting stuff here... We all have considerable experience. (Not showing off... just letting you know that what we are saying makes sense.)
If you hard code stuff into the column's code, how are you going to position it in relation to the boxes that are already there? How are you going to put it (for example) two-thirds of the way down - between the "Specials" box and the "More Info" box?
As Rob says, you can always style the box to not have borders etc.
I use the shopping cart sidebox (configured to appear only when there is something in the cart, and I have "Edit Cart" and "Checkout" buttons in this sidebox - put there by a simple edit to the sidebox's code.
See it in action here (add some products to the cart, see how it works...)
(elsewhere in this forum I explained how to add these buttons to the cart sidebox, but I can't remember where that post is... If I find it I'll come back to this thread.)