Not sure if the cannondale headset is 1.5", I think it's a bit bigger. But adapter cups are available. My super V runs adapter cups and then a normal 1 1/8" headset. If needs be you can get cups machined up. If you want to go this route I can take measurements of one of my spare ones. I've got one of Martyn Ashton's ones lying around somewhere.
These were slightly different as the hole was drilled off centre so you choose two different head angles.
I will try and take a photo of mine when I have a spare minute, although probably won't be until next week.
Cannondale Super V, Cannondale F700, Raleigh Dyna Tech (steel) frameset, 2 Rotwild frames 1 swingarm!, Diamond Back (Iron Horse copy) frameset, Scott LSD World Cup