Place garlic in small ovenproof container; pour vegetable oil over top. Bake in 350°F oven until softened and browned, 40 to 45 minutes. Let cool. (Make-Ahead: Cover and refrigerate for up to 5 days; drain before using.)
In large bowl, mash garlic into paste. Add cream cheese, sage, Dijon mustard, salt and pepper; beat until smooth. Transfer ½ cup to separate bowl and mix in Cheddar cheese, chopped walnuts and port.
Line 4-cup glass measure or small bowl with plastic wrap. Spread cream cheese mixture in bottom. Spread with Cheddar cheese mixture, smoothing top. Cover with plastic wrap and refrigerate for at least 12 hours or for up to 3 days.
Remove top piece of wrap and turn out onto serving plate. Remove bottom wrap. Garnish with sage leaves and walnut halves. Serve at room temperature.