Just partially flood it! Since you can't dewater the thing, instant negative buoyancy!
What is your aversion to just diving dry with it all the time and not changing a bunch of stuff? Can you swim a flooded unit up with your current configuration in a wetsuit? Get a super lightweight undergarment for warm water, and whatever you have now for cold water and just dive dry when you're on it. I tried doing the wetsuit/drysuit thing for both rebreather and cave. It's just a pain dicking with stuff all the time. Since I've started doing both dry exclusively, it's been much more enjoyable.
Diving dry all the time has additional risk beyond diving wet. I don't have to worry about tearing a seal on a wetsuit. If I'm diving somewhere warm, I'll probably wait until it's somewhat close to time to dive to fully suit up. If I tear a seal then, it's at least a pain in the butt and potentially a day-killer. If I'm flying to dive, it's a lot easier to carry a thin wetsuit.
I don't know if I can swim my rEvo up with a flooded loop. I do know that I expect to dive dry any time I'm doing a technical dive. But, if I'm (for example) just doing a day on a 2-tank recreational charter down in NC, the diving will be NDL diving, the water is (usually) warm, and I'd prefer to dive wet.
If I flood my loop, I believe my Nomad XT wing has adequate lift to still get me up. If the loop floods AND my wing has a catastrophic failure AND I can't swim it up AND I am unable to use my SMB to help me swim it up AND my buddy is not able to help, then I reckon I might have to unclip my BO, ditch my rig, and swim up holding a BO cylinder in one hand.
That may sound like I'm being cavalier about it and I don't mean it that way. Before I did my rEvo training, the question of diving wet or dry was a big one to me that I talked to my instructor about. That conversation convinced me that diving wet, at least for recreational dives where I'm not carrying a ton of BO cylinders, is adequately safe. If I flood the loop, my wing has enough lift. If I don't flood my loop, but the wing fails, I CAN swim it up (and have done that, in class, to verify). If the loop floods AND the wing fails catastrophically, then yes, it's a more serious problem, but that many failures is not something I would normally plan for, and there are options, even if it does happen.
What is wrong with a weight belt? For only 5 or 6 kg it will be like it is not there. Or a couple of blocks of solid on the waistband even?
Two buckles in my front. 2 straps around my waist. A lot of clutter that I don't want IF I don't NEED it.
I may fix a pair of weight pouches on my rig's waist belt, up against the back plate, if it comes to that.