Your FI rating gives you no privileges in respect of instruction conducted in a glider. The hours flown in a glider are not valid in any respect towards your SEP rating. It is therefore reasonable to deduce that instruction given in a glider will have no validity whatsoever towards revalidating a JAA FI rating.
If however you are instructing on motor gliders, and have a TMG rating in your licence, the hours should be creditable.