Also worth checking out the Dimension Pro wiki!
http://dimension.technetos.com/tutorial/ Dimension is a breeze once you know your way around. The traditional amplitude ADSR can be found under the Amp Modulator tab:
Then make sure the Amp Envelope is ON:
You can then right click within the Envelope area to make new Envelope 'Nodes'. Create any custom ADSR shape you want.
Also worth noting hotkeys:
S - Turns node into a Sustain Node (Vertical orange line appears on node)
N - Toggles Envelope Segment shape (Used in the screenshot for the release segment)
Save your new program or edited ADSR program as a new Program within the File I/O menu.
Enjoy!