it's really not that hard...
as cyanogen wrote quite at the beginning: we are free to use fastboot to JUST FLASH THE SYS IMAGE! No spl, no radio, no boot and no recovery is needed for this.
1. download System Image signed-dream_devphone_userdebug-img-14721.zip from HTC
2. extract the system.img from this
3. boot into fastboot mode
4. fastboot flash system [yourpath]system.img
5. reboot to recovery
6. flash cm update.zip
I came from 18.104.22.168 did not wipe and had no probs.