That's what we ended up doing...just ran a wire from audio out on the 665 harness back to the MP3 input cable in the trunk...works great!
I'll take a picture of where I mounted the antenna, too...tried it in two or three different spots, and always had a 'dead' spot when facing a certain direction, or when we were riding 2-up. Finally mounted it on the front deflector right under the windshield. If I remember correctly, I got that tip from Dave & Teddy!

Works great!