It's been a while, but IIRC I did my USB install this way:
With the USB stick plugged in, booted from CD with bootcodes base norestore waitusb=5
Opened a terminal, typed 'usbinstall ' [no quotes] at the command prompt.
I think it requires that you have a root shell, and that you download an extension or two. I used the ext formatting. WARNING: THIS WIPES OUT EVERYTHING ON THE USB STICK.
The install makes the USB stick bootable, installs TC itself, and creates the tce and tce/optional directories.
Once the install completes, you can download extensions via the appbrowser, and they will be saved.
I've never used partimage, Did you try to activate it through the command line, or via the applications or on demand menu (right click on desktop to get this)?