I don't think there is unfortunately.
I haven't tried it but if you copy your save file onto an SD card and delete it off the Wii's memory, when you start up Strikers it will probably want you to create a new file. Close the game and save that save file onto an SD card as well and delete it off the Wie's memory. Now you have different save files on your SD card. When you want to play you copy your file onto the memory and when your brother wants to play he copies your file to the SD card and puts his file on the Wii.
It is a lot of mucking around but it may work.