First, some findings about rovings and ribbon tape:

• Rovings are not easier to handle. Actually it's even a lot harder, because they don't come "in shape". I've created a "nozzle"-like tool to help arrange them in a sleeve, but that didn't help much.
• Ribbon tape is easier to handle, but it has polyester woven in for stability. That's bad because polyester has a low melting point and I don't want to risk having molten plastic in my plate.

So what's left? Carbon tube maybe. It's woven, contains nothing but carbon, and should be easier to handle than rovings. The diameter and per length resistance can even be adjusted a bit. I'll try that next.