AFAIK you have at least 3 alternatives:
a. Activate the hack "Region Free Channels" on Priiloader; or
b. Convert the WAD to NTSC-U (or Region Free) with ShowMiiWads/FreeTheWads/etc; or
c. Install the WAD in a emulated NAND and launch it with Neek2o/USB Loader GX/Wiiflow/etc (recommended alternative).
Keep in mind that you should probably also force the video mode; if you choose the a or b alternative, you can use an old launcher called Triiforce if needed (I remember that I'd use it fo
r launch Super Mario Picross PAL on my NTSC-U console, forcing video mode to PAL).