Though Google Play does not present Whatsapp if you are connected from a tablet, it is very easy to install it if you have another number of mobile.
You have to go to the official page and download WhatsApp's application in format APK.
I use a Lenovo Idea Pad, without SIM, but you can use the galaxy tab, a samsung, BQ, etc. You have to connect to the wifi so we do not need 3G connection neither SIM.
Then install the application downloaded from the browser of your tablet, accept everything and then it will ask you for a telephone number. Simply use the number of a mobile where you are not going to install whatsapp. Also it is a good idea to use the fixed number if it has SIM.
This way, you will receive the message of confirmation in another place but you can use it to confirm the one that you are associating with the phone number the tablet. And voila!
Simply you will not be able to use this account in two places simultaneously. Always you will be able to share this tutorial in facebook and G+ two lines down below.