Maybe something that creates a deep gravity well ahead of the ship to "drop" us through space.
I like the gravity well idea. I've always theorized that if you cored the earth and jumped in, you would pass the center and keep going. Of course, you'd ultimately approach the other side of the earth and then get pulled back in.
The solution: Take an earth-sized planet (mars is close enough) and halve it like a grapefruit. Core the halves, aim the flat side in the direction you want your spacecraft to travel, and drop it in from the other side and you're on your way.
Haven't heard back from NASA on that yet.