[Brian]

The synchronization setup we have works best when you're pushing information that originates in OmniFocus to iCal; what you're trying to do is possible, but you're pushing the envelope. :-)

Here's what I'd probably do:

1. Make a placeholder context in OmniFocus for each of the calendars you have set up in iCal.
2. sync information over from iCal, which will add the info to those placeholder contexts in OmniFocus.
3. process the information, assigning the actions to the 'real' projects and contexts you want to use in OmniFocus. Eventually, you want those placeholder contexts to be completely empty.
4. sync information from OmniFocus -> iCal
5. nuke the placeholder contexts.

Does that work for your purposes?