Honestly, your best bet for large prey is a cockroach. They're almost entirly made of calcium and protien.
Between the mouse and the anole, however, I'd go with the anole. Mice are very high in fat, which scorps have a hard time digesting. And while both would pose a threat to a scorp, the mouse would be much more dangerous.
Emps WILL kill a mouse if it annoys them enough. As a matter of fact, I once wrote a story on what one of my Emps did to and ADULT mouse on this forum. In a nutshell, it made him mad and he crushed it's skull. Of course, he was well fed and didn't want to eat it, but he killed it with ease and it did fight back viciously with no success. The only time before, when I has seen an Emp kill an adult mouse, was at a friend's place and his started to eat it after stinging it (yes, you heard me right, the Emp will sting prey of this size). Of course, being the scorp lover that I am, I recommended he remove the mouse immediately and give them more suitable food...he did.
"reach down your hand in your pocket, pull out some hope for me"