With JBOD drives there is really only one way out of the situation - backup the data to another device and then replace the drives - or - replace the drives and "re-rip" the data, and to answer your question, the USB port only supports a printer or a UPS. It can be made to support a disk, but that usage is neither sanctioned nor supported by D-Link.
Be warned however - the situation you find yourself in has grave implications. With a JBOD configuration, failure of either drive can result in loss of ALL your data, and without the backup that it is clear you do not have, you will be back to square one - you need to find a way to back your stuff up, and now might be a good time.