Thaw CocoWhip according to package directions.In a small pot, combine berries, sugar and lemon juice. Stir to combine.Place over medium-low heat and bring to a boil stirring frequently. The berries will "pop" as they are heated. Mash them with the back of a spoon as you are stirring to help break them up. Once mixture comes to a boil, continue boiling for 10 minutes. Stir occasionally and continue to mash the berries. Remove from heat.Optional: If using blackberries or raspberries and you don't want seeds in your mousse, press the mixture through a fine sieve. This is easiest when it is still warm.Allow berry mixture to cool completely.Transfer berry mixture to a mixing bowl. Add about 1/2 cup of CocoWhip to the berry mixture. You don't need to measure this – just a big scoop. Mix the scoop of CocoWhip into the berry mixture to "lighten it up."Add the remaining CocoWhip to the berry mixture. Gently fold it into the mixture until everything is combined.Gently fill ramekins or silicone molds with the mousse mixture. Freeze at least 4 hours. If making ahead, cover with plastic wrap.Serve with fresh berries and additional CocoWhip if desired.