you can shadow swing and just concentrate on starting each swing with the leg loading and a push off the ground instead of just swinging your arm around. The leg loading should be the starting point for a standard rally ball. If your leg is loaded then there's a good chance that you'll be on your way to a kinectic chain that goes up all the way to the racquet, otherwise you'll just be using upper body only or arm only.
look at the 'bionic serve' video on youtube. it deals with the serve mostly but has good info on the energy transfer involved in the kinetic chain and how coordinated movements produce more speed and power. it's a good vid.
Yonex VCore 100s - SW 351 6pts HL Tour Bite / Luxilon 4G 16 @ 51lbs