If you're considering creating your own skill based on the Flash Briefing function, you can use an alternative Spreaker podcast's RSS Feed to achieve that.

Indeed, you can limit the number of episodes from your podcast by adding the number of episodes you want, appending `/items/NUMBER` to the current RSS feed URL, and defining a number in the path accordingly.

Example:

To get more info about developing a Flash Briefing Skill, you can read the dedicated Amazon Documentation.

Sources