It appears as though Verizon and AT&T have not totally killed of Download Booster after all. It seems that it is just pretty well hidden. You can actually install a custom launcher like Nova. You then need to enable the system shortcut within the Launcher's settings. You can actually toggle it on and off once this is done, however the setting will not actually work. It won't actually merge your 4g and wifi to increase download speeds. It looks like we will have to do a bit more digging to find out how to turn this setting on. More than likely this will be a system modification that will require root. There are plenty of developers working on a Root method for the device, but for now it doesn't look like we will be able to use this feature.
Via XDA