Spray or brush the inside of a loaf pan lightly with oil and line with plastic wrap. Smooth out any large air bubbles or wrinkles, and leave some plastic overhanging the sides for easy release.
Place egg yolks, vanilla, 2 T sugar and lemonade concentrate in mixer bowl over simmering water (do not let the water touch the bowl). Use a whisk to mix yolks and other ingredients until the mixture reaches 175 degrees, approx. 3-4 min. Transfer bowl to mixer and whip on high speed until very light and fluffy and thickened, approx. 8-10 min. Gently fold liqueur and zest into whipped yolks, then transfer to a large mixing bowl. Using the same mixer bowl and whisk, whip the cream to medium peaks (should hold a peak but not be stiff or dry-looking). Gently fold into egg yolk mixture.
Wash and dry mixer bowl and whisk attachment. Place egg whites in bowl and whip on medium-high speed until foamy. Add the remaining 3 T sugar in a slow stream while whipping. Continue whipping to a shiny, firm peak meringue. Gently fold into yolk-cream mixture, adding berries halfway into the process. Transfer mixture into the prepared pan; lightly tap against the counter to remove air bubbles. If needed, use a spatula to smooth the top. Cover tightly and freeze overnight.