Preheat oven to 275ºF. Lightly coat a baking sheet with cooking spray. Melt the butter in a small saucepan over low heat. Stir in Worcestershire sauce, salt, garlic powder, and cayenne powder. Rinse the seeds with cold water, discarding any stringy pulp. Dry the seeds completely and toss with butter mixture. Spread buttered seeds in a single layer on baking sheet. Bake for approximately 45 minutes, stirring every 10 minutes, until the seeds are dry and toasted. Cool completely on baking sheet before storing in an airtight container.