I made this based on Mensink's excellent Tensioner for the Tevo Tornado. However, I found that on my Tornado, when i hit 'Home' the extruder tends to hit the protrusion so I decided to re-design and move the adjuster to the side and to the back.
There are three parts to this design but it was the only way i could think of doing it without the need for support.
I had also already printed the excellent Steam Valve knob remixed by Madizmo https://www.thingiverse.com/thing:2790738 for use on my control box but unfortunately I couldn't take the current knob off so I decided to use it for this design instead. It would be a great shame to waste it after all.
However, using the steam valve knob takes a bit of work. I used, what I think is a M5 / M6 bolt - not quite sure which one so I included a picture with measurement, then i simply cut the end off and screwed it on the steam valve and fixed it with superglue. The bolt screws on perfectly without adjustment to the steam valve knob.
For the rest of the Ikea mirror holder, I used the holders from XapaPrime https://www.thingiverse.com/thing:2796469
update 10/03/2019 - I have added a simple M6 bolt, to make it easier. Printed using Cura 3.6 Normal setting (layer height 0.15mm) and I have increased the infill to 80% for added strenght.