When I was "testing" a new intake system I made my own bracket to hold the filter up and stationary... here's basically what I did.

Went to Home Depot, bought a lumber joining plate... rectangular steel piece with numerous nail holes in it that sits between two pieces of lumber, end to end, and keeps then joined together when nailed to them. I bought this because of the numerous holes = numerous screw hole options.

Looked at the far left mounting hole for the stock airbox, bent the joining plate to form a lip to sit flush over the mounting hole, then sat the intake and filter over the new mounting bracket (joining plate). I measured how long it needed to be to reach and slightly bend through the air filter clamp, then cut a diagonal piece off to form more of a "bracket" type look.

Here is a VERY rough (thanks MS Paint!) illustration of what I am talking about: