The Bardic Fascinate song gets its DC from your Perform skill.
You can continue to increase your Perform skill as a cross class skill up to skill = Level +3 as long as you have at least 1 Bard level.
If you start out with 1 Bard level to splash, you'd still have the crazy high DC on your songs that every Bard has. Am I missing something, or is Bard a pretty sexy splash?