GENTLY lift the skin from one end and tuck butter and herbs underneath.
You can also brine it first. Whenever I've brined a chicken prior to cooking it always has more flavor. The butter trick also helps a lot and keeps the meat moist.
GOOD LUCK. We are 2, but may be 3. Either way, I'm going to buy a small whole turkey and spatchcock it like I did last year. It cooked very evenly in about 1-1/2 hours and was fabulous.