Sometimes searches are more easily done in the entry box, rather than the construct. Try this one out:
θεος <NOT> <PRECEDED BY> <WITHIN 1 Words> =ὁ
Oops, Jonathan beat me to the entry box answer!
If you do really want to do a construct search, its a bit more complicated to get accurate results. Here's the best I could come up with:
Screen Shot 2014-04-15 at 5.13.28 PM.png 53.46KB
Basically, we are searching for any span of two word before θεος, but the middle word can't be the article. You have to set your Scope to chapter or book, though, or instances of θεος at the beginning of a verse won't be found.
But as you can tell, its much more complicated - I strongly recommend the entry box solution for queries like these.