Gary

If it is a hard Hysol then the amount of heat required to soften the epoxy would also damage the fibreglass, if normal 5-30min epoxy I would personally sand it as you would not be able to put any amount of heat in to the epoxy again with out damaging the glass work. Sanding the epoxy off will take time but I think this way is the safest way also if you soften the epoxy you would not be able to sand it whilst soft.
If it is normal resin and you do want to have a go with hairdryer only I would mix up some of the same epoxy let it go off and apply heat to see if it will peel off etc I think I would go for a very sharp X-ACTO blade and try and slice it off then sand with 180-320 grit

Alan