After trying around a lot, I discovered this easy method of installing WhatsApp on an iPad (or iPod touch). You don’t need an iPhone or any configuration utilities. Just a jailbroken device with Installous.
If you face errors finding WhatsApp within Installous, go to Settings (within Installous) and disable the “Only Show iPad Apps” option. Also, try clearing the Cache or rebooting.
I’ve personally tried it out a few days ago and it worked exactly as mentioned. You can also read the text version of the tutorial.