DAC is available in Express, it's just disabled by default.

http://blogs.msdn.com/sqlexpress/archive/2005/09/08/462609.aspx

Steps to enable DAC in Express:

1) Launch Services Applet in Control Panel

2) Stop SQL Server Express Service

3) Launch Properties dialog of SQL Server Express Service

4) Add "-T7806" to the startup parameters

5) Start the SQL Server Express service