MyBookTable has a custom JSON import/export tool you can access from MyBookTable > Import Books. You can find a description of the JSON schema on our developer wiki here.
By the way, we support 13-digit ISBNs, we just pull the canonical ISBN provided by Amazon through their API when importing from there, which is often 10-digit for whatever reason.
~Tim
https://github.com/authormedia/mybooktable/wiki/Custom-Import-Export