Currently there is not a way to actually hide a material. You can give the appearance of an invisible material by making a custom material with the opacity map being completely black. It would visually hide the material for rendering purposes but it will not physically hide it when you are modeling in D5. In order to get to your canvas behind the glass, you would have to hold your space bar and slightly move forward to get to it. Using the clipping plane sometimes helps in that situation too to change materials that close to each other.
Thank you for your answer.
Even if it’s not necessarily what I wanted to hear.
The D5 team is doing a good job.
That’s why I assume that there will be a solution soon.