Question: I've read several of the migration guides for moving an existing windows install from a HDD to a SSD.

Steps are basically:

1. Attach external drive
2. copy hdd image to drive (conezilla)
3. install ssd
4. boot to clonezilla
5. copy image from external drive to ssd
6. boot from new ssd

My question is, can it be done like this:

1. attach ssd in an external harddrive enclosure
2. boot to clonezilla
3. copy image from current hdd to ssd (via enclosure)
4. install ssd
5. boot from ssd

Thereby saving an entire image copy?

Answer: 
Yes you can clone directly to a SSD and boot from that drive. I've done that a number of times and never created an intermediate image. The only issue sometimes can be partition size difference but programs like Clonzilla should be able to handle that as an option.
You can do it, but it will still take hours upon hours to complete. You might as well just do a fresh install.