No - there is no easy way to just tell iCloud to omit part of the camera roll. I suppose a jailbreak could theoretically work in this functionality but I'm not up on what is possible in that realm.
Two workarounds seem practical today:
- Manage those videos in another app (Vimeo/iMovie seem clunky and undesirable for this but perhaps something like DropBox would work if you didn't mind the extra steps of migrating and then deleting video assets from the roll).
- Give up iCloud backup of the camera roll contents and depend on iCloud Photo Stream for eventual backup to a computer.
I've seen the second option work for people once they were acquainted with how the archival process works on a computer pulling from Photo Stream. Since iCloud backup is usually a half day behind in backing up, the stream is generally faster at getting a still photo off your device than the backup mechanism.
If you are OK with a computer regularly importing the photos from the stream before the 1000 image / 30 day limit starts deleting them from the stream, you could turn off the Camera Roll from your iPhone's backup options:
Selecting Turn Off & Delete will reclaim your space in a minute or so. Just be sure your current camera roll has been totally imported before selecting the red delete option.
Since videos do not go to the photo stream, you will need to transfer them off your device to make a backup copy of them going forward when needed.