SQL2008 shared hosing login permission

[Antony]

Hello,
for my mssql shared hosing I have create a database and login using
security settings write by microsoft for sql shared hosting:

http://learn.iis.net/page.aspx/530/sql-2008-for-hosters/
http://download.microsoft.com/download/d/1/f/d1f05c2e-0741-442d-859e-9417b377fdfa/The%20architectural%20view%20of%20SQL%20Server.zip

but trying to publish some applications I got the following error:

Cannot find the user 'dbo', because it does not exist or you do
not have permission.

I found that the sql that generate the error is:

CREATE ROLE [aspnet_Membership_BasicAccess] AUTHORIZATION [dbo]

I have seen that adding on database the db_owner rolemember for
userlogin the problem is solved but this feature is not included in
the microsoft documents for shared hosting I think for security
reason;
On documentation for SQL2008 shared hosting Microsoft set only
(db_ddladmin, db_datareader, db_datawriter)
my problem is to find a way for add CREATE ROLE command to user login
without give it the permission for ALTER DATABASE;
with ALTER DATABASE user can modify database size or can open security
problem and I don't want this.
do you know if there is a way to solve the problem?

thanks and regards
Antony