Plesk 12.x / Windows :: Create Subdomain Without Creating Main Domain

I am using Web admin edition .I need to create two subdomains namely sub1.example.com and sub2.example.com with different IP address. So i need to create two webspaces since a webspace cannot have two domians pointing to two different IP. So now to I can create two webspaces set to different IP. But to create sub1.example.com in one webspace and sub2.example.com in another webspace , i need main domain example.com in both the workspace. But if try to create example.com in second webspace it already exists.Because it exists in another webspace. Actually i dont want to create example.com in both webspace. i need to its subdomain in different webspace.

So one solution is to create example.com and sub1.example.com in one webspace and create another webspace using Adding new webspace and specifying domain name as sub2.example.com. But i don't know does the second subdomain will work properly without creating main domain.