After a series of tests I have built a BLH-1 battery dummy for Olympus cameras (currently the OM-D E-M1 Mark II). Since the battery is larger than other models, the lid of the battery compartment is also bigger. This allows to cut a slot for the cable to pass through while the lid is closed. You shouldn’t do this to the original lid. That’s why I currently try to get spare battery compartment lids for the camera.
You may find more details about battery dummies on my Battery Dummy Page.