How do I create a cutoff envelope in X2?

ULTRABRA
I'm also struggling with this same topic.  I checked the video out but it didn't give the answer.  I believe I'm trying to do the same thing as the OP - I have a soft synth and I would like to control its cutoff frequency using Sonar X2's automation.   I just cannot figure out how I make an envelope which will control the part of the soft synth that I want it too ... could someone give some step by step instructions?  Thanks ... 

You do the same thing as shown in the video, but substitute the parameter you wish to control.
 
EDIT: the video link I posted above doesn't work properly in IE by the way, in Firefox you get a set of three videos, in IE only one :-(  Not sure about other browsers.
 
For example, insert soft synth -> Rapture, chose simple instrument track.
Choose a patch which uses filter 1 cutoff, e.g. 60's Electro 1 (under sequences)
Write a 4-bar note so you can hear the arpeggiated patch playing.
Click the Automation Lanes button on the track.
The Automation Lane will initially display Volume.
Click that and select Rapture-> then navigate to the filter 1 cutoff for element 1.  Rapture's parameter list layout isn't exactly intuitive, so it is: Rapture->Decim On/Off 03 - Filter 2 Type 03 -> Filter 1 Cutoff 01
Now that automation lane is set up to control the 01 filter cutoff in the E1 element of Rapture.  You can hand-edit the automation information or use write-enable and move the control (in Rapture's UI or via a linked controller).
Do as above for any other synth/parameter, the only problem might be locating the right parameter in the parameter list, sometimes they're just given as numbers.
 
What I haven't been able to work out is how to get Sonar to write automation information for an arbitrary synth parameter using 'write enable', if that particular parameter hasn't been pre-selected as an automation lane target.  Let's say a synth lists its parameters as '01-99' or something.  How do I record the movement of the parameter I wish to control using write enable as a means to identify it if I haven't already selected it?  Can this be done?
 
EDIT 2: Ah, this thread holds the answer.  It's a bit clunky and limited but does the job more or less: http://forum.cakewalk.com/SONAR-refuses-to-record-automation-m2638267.aspx
 
At the very least it's a means to locate the plugin's parameter in its automation list :-)

(I'd still quite like to know whether it's possible to write arbitrary automation data though).
 
Ah, finally twigged it - you have to click the Automation Write Enable button on the synth property page, not the track!
So, an alternative answer to the OP's question would be to write-enable automation on the synth's property page and move the desired control (e.g. cutoff) you wish to create an automation track for.  This will create some initial automation data.  Then hand-edit the data as required.  Click the track's 'Automation  Lane' button to put the automation data in its own lane for easier editing.