Download the Orasi Support Document - Quality Center - How To Setup A Proxy For The ''sa'' Account To Install And Maintain QC?

If you can't get the document, here is the SQL, provided as-is with no warranty, etc. etc.

/*****Run this sql to create the sa proxy user if using the sa login is not allowed *****/
USE [master]
GO
CREATE LOGIN [qc_admin_db] WITH PASSWORD=N'qcadmin', DEFAULT_DATABASE=[master],
CHECK_EXPIRATION=OFF, CHECK_POLICY=ON
GO
EXEC master..sp_addsrvrolemember @loginame = N'qc_admin_db', @rolename = N'dbcreator'
GO
EXEC master..sp_addsrvrolemember @loginame = N'qc_admin_db', @rolename = N'securityadmin'
GO
/*****Run this sql after QC is installed so that future reinstalls QC run without permissions
error *****/
USE [qcsiteadmin_db]
GO
CREATE USER [qc_admin_db] FOR LOGIN [qc_admin_db] WITH DEFAULT_SCHEMA=[dbo]
GO
EXEC sp_addrolemember N'db_owner', N'qc_admin_db'
GO