I also have installed a cone type air filter directly to the turbo inlet. I removed the oil separator from the stock air filter housing using a small chisel (can opener action). Currently, the canister still sits above the turbo where the air filter would have been. I would eventually like to cut back the oil return line and drop the separator canister out of site.
I agree with dieseldiehard's observations relating to increased turbo whistle/whir after replacing the filter; in fact the sound is quite pleasing!