how to add 2 static blocks to a category page

Question

i have a staic block called "sub categories" and i have this set to all my parent categories so when you click on them it shows the sub categories. However i also want to add another static block to the parent category to show the products that are on sale. I already have the On_sale static block created and correctly coded i just dont know how to add it to the parent category as there is only 1 drop down box for the static blocks.

Question: how to add a second static block on a category page?

Thanks for any help.