The attached worklfow shows how you could do this!
Essentially, before your final output you can use the sample tool to get the number of blank rows you want. Then use the multi field formula tool. Select all of your fields and make sure you uncheck the option to create a new output. With that option deselected, you will be updating your existing fields. Your formula should just be NULL(). Then union this field back to the rest of your remaining output. The union tool has an option that lets you order by the input so you can choose to put the blank row at the beginning or end.