Why do you need to minimize soil/medium surface disturbance? I have a 5 gallon bucket that I put a nipple on and have 4 feet of vinyl tubing attached to. I mix up my nutes with the tube laying on top of the buck and then put my thumb over the end and water away without any concern for any "disturbance" to the surface of the coco/perlite mix.
I have a 3x3 grow and I have two 2g pails for mixing. I hand feed with a 1L measuring beaker. I pour evenly from either side, or around the edge, then get my mitts in there to even out the pro mix. It's not messy.
I mulch the top layer of my containers with straw and pine bark nuggets. Under the mulch when I build my final size blooming pots I like to add some fresh earthworm castings as a top dressing and then a sprinkle of diatomaceous earth to stave off any gnats & such. The pine bark nuggets and straw help to both retain moisture and prevent the soil from dipping in and exposing roots when I pour from a watering can. The DE also provides a source of silica once it breaks down.