you can play every single emulator without installing even 1 bit of software on your wii. it will remain completely virgin.
put the roms and everything needed for the emulator on the SD card.
put the boot.dol of the emulator on the root of the SD card
start the dol with bannerbomb.
you can also use loadmii in the equation if you want things to be a little easier switching between emulators.
everything is done entirely in RAM and no permanent changes are made to the wii, so whenever you exit the emulator or turn off the wii, your wii still has its hymen intact.