cthulhia | bricks?

so... over the summer I started using some wooden planks on my radiators, making them into highly coveted horizontal space. However, I kinda want to turn the heat back on. Like, soon. Would it be sufficient to use bricks or cinder blocks and just elevate the planks? Or do I need to just give up that space until spring again?

And, if the former is ok, where do I buy small quantities of bricks?