Not everyone has access to fresh blueberries no matter what time of year it is. Some areas just do not have that sort of thing. So, you can definitely use frozen blueberries in any dish. And using cake mix in a box will certainly save you a lot of time and work.  Just buy a lemon cake mix and make it as directed, adding the frozen berries to the mix after everything else. Make sure they are still frozen when you add them, or they may get mushy and turn the batter blue.