Probably ... Jeff Geerling has done a fairly good review that includes a photo of the One Up with the bottom half of the case removed. It looks as though the fan should be removable ... or at least you could cut the wires.
There is a small white LED to the right of the camera that warns you that it is on. The LED comes on even when the shutter is closed, which led me to think the camera ought to be working, even though the shutter meant there was no image.
It would be really nice if that LED changed colour -- say red when the shutter is closed and green when it is open (and off when the camera is off, of course).
The 500+ is £228 (including 20% VAT) here. The CM5 (no flash, 8GB RAM, With WiFi, as in my One Up) is £108.
The cost of the One Up shell (without the CM5 or SSD) should not be affected much by the current silly memory prices. It isn't in stock anywhere that I can see, though.