I don't know length of travel for Atlas cross feed, compared to 150 readout travel. A breakaway is a good solution, two better yet. Locate center of travel for slide, center the DRO on that.
Extension springs and stops come to mind, but stability is gone.
Another might be mounting glass on a linear guide 'spacer'. A nylon pointed grub could set minimum friction that would slide on contact?
Whatever route chosen, you definitely don't want reader and ends forced into each other.