Currently the best way is to add external subs is to add them as a special.
1) Remove the sub-file from your mylist
(or you can't delete the entry - IIRC ^^)
2) Remove the sub from the db
(because you can't have the same file twice in the db)
3) Add a new Episode, check "special ep" and name it something like "Softsubs" (EDIT: enter 1 as ep-number)
4) Re-add the file with the subs to this new entry
[ 5) Either add the corresponding RAW to ep1 or request a change for the existing ep if it's in fact "jap/none" and not "jap/eng"

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