Two solutions are widely adopted. You can simply put up with with the sloppy cutouts that you make yourself or, in many instances, you can purchase pre-scored foam from the factory. This allows you to make pockets for your equipment just by plucking out the appropriate pieces of foam.

Diced foam tends to fall apart with use.

One difficulty with these usual solutions (over and above their amateurish appearance) is that the fit will likely be poor, perhaps causing you a great deal of frustration each time you try to withdraw something from a tight-fitting pocket. Another shortcoming, particularly when using prescored foam, is that the case insert gradually falls apart with use. A further worry is that the foam typically found in hard cases is quite soft; so heavy items could easily bottom out in a fall.

CaseCAD solves the problem for you.

Up until now, those who weren't content with sloppy cuts or pockets plucked from a grid of pre-scored foam had few options. One was to hire a custom case manufacturer to solve the problem for them. Another was to purchase (and learn to use) a general-purpose CAD program for drafting the mechanical design and then to order foam cut according to this pattern—a strategy that requires considerable acumen, patience and money. No wonder that few people attempt it.