Possible? Two diferent pages. Same subdomain on diferent domain.

Hi,

Is it possible to have two diferent sites like this:
1.) pizza.maindomain.com
2.) pizza.seconddomain.com

If I set up new site pizza.maindomain.com and then want to set up pizza.seconddomain.com, wordpress returns "Sorry, that site is reserved!". But if i make secon site like "pizza2.seconddomain.com" and change its domain using "domain mapping" to "pizza.seconddomain.com" it works.

I would like to do this without using "domain mapping plugin"