CMPTLaunchMenu() has to be used instead: https://wut.devkitpro.org/group__nn__cmpt.html#ga5b56484b59eaf8b0a2e37b4ddca68919. Thanks for the suggestion!
I have updated Boot2vWii with these changes and you now have to pass the whole TitleID to the make command ("TID=")! Just combine TIDLOW and...