How to draw many ink splats on the ground in real-time on mobile?

The player can contol a ball and that ball should leave a trail of ink splats behind. The number of splats can be very high so I figured it would scale better to draw them on the texture instead of creating objects/projectors for each splat. (I don't need to access the individual splats later anyway).

The problem is that SetPixel is very slow. I I want to have splats with at least 64x64 textures that's 4.096 SetPixel Calls (SetPixels doesn't help much as I'd have to get all pixels from the existing texture beforehand) which causes noticable lags.

I tried the CopyTexture function from the new Beta but it doesn't seem to be much faster and it doesn't work well with transparency from the splats.

So do you have any idea to approach that?