Hi, you certainly can do. The Trill sensors can detect touches through certain thin non-conductive materials up to a couple of mm thick.
Vinyl for example is good for covering the sensors or thin acrylic works nicely too. In a past project we also added a series of physical notches on a Trill Bar sensor using some Plasticoat liquid rubber and a stencil. This was really effective and hard wearing. The trill bar was used as the strumming interface for a digital guitar instrument and the physical notches gave some tactile feedback as to the string position on the sensor. Here's a photo of how it looked: