Caching grammars

I must parse documents that may use a large number of fairly large XSDs.
However, the large majority of documents will not use most of those XSDs.
Therefore, I would like to use a custom LSResourceResolver to resolve the
target namespaces to local resources during parsing rather than building a
Schema object that has all the grammars loaded up front.

Unfortunately, as nearly as I can tell, grammars loaded through the use of
a LSResourceResolver are never cached in the grammar pool. Is that correct?
Is there some nuance I'm missing?