Go buy a fairly inexpensive piece of jewelry....like a $50 necklace or some crap. Do the Olive Garden thing, act all nervous, make a big deal out of it. She'll be expecting you to propose, women aren't stupid. Give her the diversion piece at dinner, with the whole preemptive "I love you so much, blah, blah, blah" thing. Sure, she'll feel a little stupid for thinking it was the big moment, but she'll get over it when she gets home and finds a rose (fine, Mike, a snake!) on her pillow with the engagement ring. At that point, the expectation will be gone and she'll be truly surprised!