I knew the punchline before even starting! Impressive number of theme entries throughout the grid (do I detect a Qat usage?). Shame about unchecked cells and 2-letter entries, but I understand that feeling of wanting to completely fill a grid with an idea!
Qat's an online tool for searching dictionaries based on more complicated queries. Here's one based on your constraint, assuming a 4-letter grid entry and using the default dictionary (I think you got them all, except for (TRES)PASS).