You can't do it that way. Create the item using just the final component of the name (after the last ":", "Offers" in your example), then do Edit in Projects or Contexts view as appropriate, tap on the new item, and use the refile button (looks like an file folder) to move it to the right place.
Use Help->Send Feedback (or Send Feedback from iPhone app) to make a feature request to create nested items directly like you can on the Mac.
(Brian, perhaps you can go remove the two posts by the OP and myself from the original thread:
http://forums.omnigroup.com/showthre...0527#post80527)