Ask HN: How to fake laptop connection via USB

Hope we have some USB professionals here. I have an external audio sound are device that is USB powered and needs to be connected to PC/Mac/tablet for it to power up. The device has a built in mixer that offers direct monitoring, I've audio goes from input ports directly to outputs (skipping the PC). I would like to make the device work as a standalone mixer without the need to connect to a PC. I've connected the device to a USB wall socket/charger but the device doesn't power up. I suspect that the reason is that the USB charger only sends 5V power but not the data steam (to pin 2 and 3, as presumably PC does). Does anyone know if it's possible to hack the USB cable or USB wall charger to make the audio device think it's connected to a laptop? Or phrased differently, what does the device see when it's connected to PC vs a wall charger?