BootMii Configuration Editor llows you to change the values in the /bootmii/bootmii.ini file without having to take out the SD card and edit it on a PC.

Release notes:

Added OFF option to autoboot. Setting Autoboot to off will disable the delay timer setting in the configuration editor, as this serves no purpose with autoboot disabled. Setting of OFF has the effect of making the Wii sit in the bootmii menu screen until you select the system menu or homebrew channel option from the bootmii menu using either a gamecube controller, or the power/reset buttons on the front of the console.