Marketpress - Categories Dropdown Menu - How to set custom default text?

Hello all,

I'm making a custom theme w/ Marketpress. In my store page, I've inserted a dropdown menu of all available categories. But when the page loads, the category that shows up by default isn't submit-able. The rest of the categories are, but not the default category. To get around this, I'm wondering if there is a snippet I can paste into the backend that will list the following default text, no matter which categories populate the list:

Default Text: "Select a Category"

Is this possible? Thanks guys.