It depends on the specifics.
If you are booking these conferences using TMS, then you need to configure your Advanced Conference Options. "External MCU Usage in Routing" should be set to "Always, except point to point", and "Preferred MCU Type in Routing" should be set to "TANDBERG Codian MCU".
If these are Ad-hoc conferences, then what you want is Multiway (i.e. Conference Factory). This requires a VCS however. Refer to the Multiway Deployment Guide for specifics.
http://www.tandberg.com/support/dl.php?id=1119&dir=Deployment_Guides&fn=Cisco_VCS_Multiway_Deployment_Guide_X5.pdf
L-series (T150) endpoints cannot initiate a Multiway call according to the docs, but that may have changed since the doc is a little out of date now. They can be joined to a Multiway call though (L6.0 or higher). MXPs require F8.0 or higher.
If neither of those works for you, then your only option is to setup the Codian to create a new ad-hoc conference on incoming calls to unknown conferences, and then give your MCU an H323 Service Prefix so that all calls with that prefix will route to the MCU and start a conference using that ID. Make sure that your parent Template has numeric ID registration for both H323 and SIP enabled.
The Codian by itself is not capable of forcing anyone to use it for Multisite; this seems to be what you might be thinking from the template questions.
