I know some folks have plugged the small hole for the ATO line that goes from reservoir to return section. You can use a small pump to push water from the skimmer section up, over and into the reservoir to turn into a fuge. Point the line into the reservoir down and it should get some tumbling action. Then it will fill to the top and spill over into the skimmer section and return section.
I’ve contemplated doing the same thing in my Waterbox sump. The million dollar question I have to answer is how I would want to set up a new reservoir then. Have some ideas but nothing concrete. I’ve also figured to get some black acrylic to silicone into block light from going into the return and skimmer chamber, grow light that is. Hope this helps!