This is why ORMs are bad. They make hard problems much harder, and the only benefit is that they maybe make easy problems a little quicker. The cost/savings is heavily skewed toward the cost, since there's no upper bound on the cost and there is a pretty small lower bound on the savings. Micro-ORMs tend to do a better job of not shielding you from (or rather, getting in the way of) the SQL while still providing some good result-to-object translation. Whether even that is necessary depends on your language, though. (For example, in Python, psycopg2 has a built in way of spitting out namedtuples, which means you get result-to-object translation out of the box. That makes even a micro-ORM pretty unnecessary. On the other hand, a micro-ORM that does this well without blocking you from the SQL, such as PetaPOCO, is a boon in .NET.)
If you can, your best bet would probably be to find a way to get your ORM to execute raw SQL (with good parametrization to prevent injection attacks!!!!) and be done with it. It took me way too much experience fighting with an ORM on complicated queries to realize that.
