The clamping effect of just a silicone tube isn't enough for true clamping. Even if it is tight. When clamping you need to able to alternate the pressure, to go from loose to tight and so on, with a
sleeve it's basically just one setting.
One could use a
sleeve that is not overly tight as the cushioning material for clamping. Cable clamps are readily available anyway.
I was amazed when I found them from my local "supermarket", as before that I ordered few ones from U.K.
If your hardware store doesn't carry cable clamps, I would look into marine shops.
So, overall, best to get a cable clamp or similar, I wonder if SWM still has stock of his clamps? His clamps have a really nice dialing, you can really adjust the strength precisely.