There is no great way. I find LME you add slowly, burner off, stirring so you are sure it's not sitting as sticky lump on the bottom. DME I add fast, pure dump, so that the steam coming off the pot doesn't make Spaetzle dumplings on/in the bag. If you can keep the mass away from the sides of the pot it just slowly dissolves. Since that is impossible, you just need to be patient and stir, breaking up the lumps as you see them. It will all melt into sweet wort. I have just walked away from the pot for a while after dumping and it was all taken care of for me.