Multistore mutiple group domains, without main domain

[IeM]

Can someone help,

I have a member driven shopping cart where members have their own domain names.

 

I need to have multiple domain names in a single multistore tree group but without one of the domain names being selected as a main domain. Reason: When you have a main domain say, www.main.com and you go to www.site1.com which is in the same group, the URL will be changed to www.main.com

 

For marketing and tracking purposes I need the site that the user enters to be the URL displayed.

 

How can I set this up preferably without playing with the .htaccess file as that gets updated?

 

Personally I don't understand why a main domain HAS to be set as it removes flexibility.

 

Thanks

[sadlyblue]

Also wanted to know... If you find the solution, ls post.

Thanks