Combine first 6 ingredients in a spice mill or small food processor; process until finely ground.
Add 4 inches water to a large stock pot; bring to a boil. Stir in spice mixture. Cover, reduce heat, and simmer 15 minutes. Add potatoes and corn; cover and simmer 25 minutes. Plunge lobsters headfirst into boiling water. Return water to a boil; cover, reduce heat, and simmer 10 minutes.
Place wine in a small nonaluminum saucepan; bring to a boil. Reduce heat, and simmer, uncovered, 15 minutes or until wine is reduced to 1/2 cup. Add margarine and next 3 ingredients; stir until margarine melts.
Remove lobsters from pot; drain well. To serve in the shells, place each lobster on its back. Cut the shell of the tail segment lengthwise. Insert a sharp knife between the body shell and tail shell, cutting the two apart. Crack claws.
Remove corn and potato with a slotted spoon. Place lobster, corn, and potato on a platter, and serve with margarine mixture. Garnish with fresh thyme sprigs, if desired.