There is an option 1 (implausible) to collect your firmware for DIR-300 with the cuts and functions through restoration (as in dead firmware) to flash. NVRAM should not be erased, and the firmware to order the display of data to the NVRAM. But it's hard.
Is option 2 more plausible, but needs to be clarified. The router is the loader which at startup for 1 second opens RedBoot ("loader" c orizanol TELNET and console) on the WAN port. With it, you may (read about redbut long and deep) to read the contents of nvram (part of the stick, where the roll settings). He was not engaged in any form — I don't know. Theoretically, there is only text data, so maybe we can parse, this may need the source code of the firmware (nvram)