1) Navigate to Visual Studio Tools > Visual Studio Command Prompt
2) Execute aspnet_regsql.exe -ssadd -sstype c -S [sqlservername] -d [sqldatabasename] -U [sqlusername] -P [sqlpassword]
3) Add line to web.config
sessionState mode="SQLServer"
allowCustomSqlDatabase="true"
sqlConnectionString="data source=
[sqlservername];Initial Catalog=[sqldatabasename];user id=
[sqlusername];password=[sqlpassword];"
cookieless="false"
timeout="900"
allowCustomSqlDatabase is required if you have configured a non standard database name.
[Edit] - 30th of August 2012
The [sessionState] attribute needs to be added in the [system.web] section of the web.config
References:
aspnet_regsql.exe - parameters;
http://msdn.microsoft.com/en-us/library/ms229862%28v=vs.80%29.aspx