I don't know of any commercial solutions, but a machine shop can certainly make you a set of elongated rack ears. That might have problems of its own, i.e. I think your 3750 will sag toward the back. A machine shop would likely charge you 50 bucks to make such a thing, so you might want to look at removing the rack ears and sticking the switch on a set of "shelf rails" like you'd normally use on a server. Shelf rails are basically a set of front-to-back L-brackets (one for each side) that you simply set a server on. You can drill it out and use screws as a stop, to keep your switch from sliding front and back. Or if you have a tap and die set, buy a section of solid square metal bar, maybe 1/4" squared, cut four one inch sections, and tap the bottom of those to use for your stops instead. HTH.
Not sure what the mounts look like on your particular piece of hardware, but you *might* be able to flip the mounting brackets around on the switch itself. I've done that in a few instances and it provided enough room for whatever piece o' hardware I was working with to fit properly.
Just my $0.02
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You might just put it on a universal Gruber shelf/rails with some Velcro to keep it from sliding around. I am surprised your cabinet is so shallow; you may have issues with servers down the road as well.
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