My CM3 was running around 57°C whilst idling. I found some 12mm x 5mm copper bus bar and created a crude copper block from three short lengths held together with some thermally conductive adhesive, having given them a quick clean up first with some emery cloth. Cleared a patch in the case lid (the centre of the CPU is about 35mm from the front edge and about 55mm from the left edge), placed the block directly on the processor, put a blob of thermal adhesive on top of the block and popped the lid back on for a second. The block stuck well enough to remove the lid with it held in place and I pushed it down firmly.
Once the adhesive was cured, I placed a piece of thermal washer material on top of the cpu and re-assembled it all. Idle temperature is now around 39°C rising to around 47°C when place under heavy load.
With the CM3 setup and TVHeadend installed, I am now able to record/watch Freeview HD directly using a USB Dongle (August DVB-T210) and I can finally retire my old SD only PiB with OSMC.