Can't be done -- yet
The sad answer is that you can't search for nominal clauses. In actuality, you aren't really searching for verbal clauses, anyway.
The morphological database analyzes words and morphemes. So when you search, you are limited to parts of speech, etc. Now, in the case of verbs, you can search for those words, and then display them in a column, and you can look at the "clauses". But you, the user, are actually the one who decides where a clause begins and ends. There's nothing in the database says "the clause begins here and it is a verbal (or nominal) clause." Indeed, in the case of participles, you never know if it is used as a noun, an adjective or functions as a predicate (or subject!) in a nominal clause.
You could try to search for patterns, e.g., two nouns coming together, but you would get a *lot* of false positives!
What you need is a database that tags the text according to clause boundaries and clause constituents. We're working on that...
Kirk E. Lowery, PhD
President & Senior Research Fellow
J. Alan Groves Center for Advanced Biblical Research