I designed this in Fusion 360 to hold my air freshener away from view. It hides against the centre console by the driver's seat, but could also go by the passenger's seat. The holder is designed for an Audi S4 (A4) B8.5, however it may also fit many other makes and models (you could use double-sided tape instead of the retaining clips). It is designed to hold one 2D air freshener by 'Little Trees' (max dimensions 119mm x 70mm x 2mm). I printed mine out of PLA but you might want to use something different. First, superglue the front and base together. Two retaining clips are required: slide the long end behind the trim panel against the carpet and then press-fit the square pegs into two of the holes in the front to hold in place. The retaining clips do not provide much clamping force but they have worked fine for me so far.
Print the retaining clips with a brim