In reply to siwithington:
Adam's approach is probably best, you don't actually get much speed benefit from having the image files themselves on the SSD.
If you want to work on a particular set of images while away, or are importing images on the go, you can use the 'Export as catalog' and 'Import from catalog' options. This creates a new LR catalog and a copy of the original images, which can be edited then remerged with the main library.