Connect to external DBs

I have not tried to do this. You might try checking:

https://wordpress.stackexchange.com/questions/1604/using-wpdb-to-connect-to-a-separate-database

We use the global wpdb object, so in theory you could set this to something else while rendering the db-table-editor, though there is surely some code to work out along the way. If you figure it out, please provide an example so that others may benefit.

Cheers!