You have a couple options.
Option 1: You could make a PCB with the USB connnectors on it with a 5volt regulator (PE# 7805) and perhaps PNP power transistor (PE#s TIP147 or NTE2344, etc) for more amperage. Then mount USB A connectors (PE#s 320-247, 320-248, 320-251). Then cut slits for the usb cable connection.
Option 2: You could use this connector. Normally the car chargers are held together with a screw or two. Take out the screws, the face plate should come right off, then modify the case to fit your mounting needs. For example drill a hole in the wood that will fit this snugly. Insert and glue.
Option 3: PE sells panel mount USB connectors(PE#s: 092-278, 092-279) usually meant for dishes(PE#s: 262-028, 262-334, 262-348, 262-838, etc). You could either use stand alone or buy dishes to give a pro audio feel to your boom box. Be aware that they are USB A (normal) to USB B (typically a printer type) connectors. PE also carries these cables (PE#s: 130-047, 139-080).
Option 4: Look for a laser cutting service online. It is really awesome service. You find one of the many materials (Aluminum, Stainless Steel, Derlin, Acrylic, Styrene, Silicone, Melamine finished MDF, Plywoods, Veneer MDF, plain MDF, Bamboo, Hardboard, Cork, and Leather, Cardstock, Felt & Cardboard), pick a size, upload your design with cuts, mounting holes(vectors), and engraving(raster). They then make your design and send it to you for a reasonable price. Voilâ, you have your own custom USB face plate, or control panel.
Option ∞ Actually the options really are limitless. I have only touched on a few. Look all over the place for solutions. You might be surprised where and how you find ideas for control design.
Best of luck☺