I'm waiting on a company to make a poly-carbonate carbon fibre reinforced (same material as the p4k) battery grip. Something that has replaceable batteries, Can run the camera for at least 2 hours, isn't as expensive as just having 10 canon LP-E6, would raise the camera no more than 4cm as to not get too tall and is contoured to the camera body. An important addition would be to have multiple threads on the bottom to make it much easier to mount the camera off set for gimbals.
I think going straight into the LP-E6 and remove the battery door like most common battery grips makes the most sense and I was thinking considering the cameras 7inch length you could get away with 2 sony-npf 550 batteries in some sort of tray. You can get 2x NP-F 550 Neweer batteries for 30 dollars on amazon. Have the battery tray insert from the left would make it possible to swap batteries without removing the camera from a gimbal.
2x sony np-f550 at 2600 each gives you a 5200mah battery. Let's say a single LP-E6 1800mah lasts a minimum of 45 minutes we can guess that a 5200mah battery might last roughly 2 hours and 20 minutes. Now I know the P4K has been a bit funky with run times and different batteries so tests would need to be done but I think all this would come to adding about 350g of weight to the camera and allow you to run from cheap sony batteries. Might be worth it if the price is right?