In theory, you could create an iPad email address, but that really defeats the purpose, as people would have to iMessage you at that address, and hope you are on your iPad.
I think you can turn your phone on receive at in settings to only your number and then on your iPad receive at would just be the email you want. (Settings>iMessage>Receive At)
I think you can turn your phone on receive at in settings to only your number and then on your iPad receive at would just be the email you want. (Settings>iMessage>Receive At)