I would think about what your ultimate goals are. Are you trying to reduce setup time, have fewer things to transport, shrink your table footprint, or just achieve a monolithic aesthetic? I’ve confronted this problem with a number of external devices on my videosynth, and I think spending 3U rack space on something not designed for it is rarely the most effective solution.
Velcro to the side of the case is a great strategy. (Or 3M command strips, which pick up less fuzz.) If that’s not slick enough for you, I’ve had success mounting 1/4” tripod attachments or hot/cold shoe camera mounts to the side of my case for giving non-euro gear a quick and sturdy mount point.