I had one of those. I would recommend that you stick to formula. Some of the stuff (forget the name it extremely high in calories in a small volume). Being the experimental type, I used a blender, it worked well too�. but every so often I would plug up the tube and make a major mess trying to unplug it using pressure.
Just look at the diameter of the tube and realize that near the end there is an constriction.
If you decide to do this make sure it is finely blended. Others, (Charm, one of my heroes) used the PEG to "imbibe" some wine.