I managed to fit mine into a packy. I started like i was making the medicine spoon type STP device (cut off the top part) but i cut off the "lip" part at the top also so it was flatter - left the girth of the opening, though. Stuck some tubing in that, super-glued it together, then stuck the whole thing down the spout for the device (had to cut the tip off) and super-glued the whole thing together for safety.
It worked, but i need to fine tune it. I tend to need two hands to use the whole device because the material IS very soft and i found it more likely to buckle if i didn't hold it.
I'm also trying to fit my SheWee in a packy.
On it's own, both devices work great for me. I would just like to be able to use a packy STP device someday soon.....