Some items I use are a set of smooth jawed forceps (sometimes called Hemostats—they have no teeth to damage delicate PE) You can usually find them at Micro-Mark, or at electronics supply stores. They will lock so you won’t be dropping the part accidentally. The other tools I use is are a Crescent smooth jawed electronics plier that comes in a set of 2 electrical tools from Home Depot (Lowe’s might have them too). They are inexpensive, and are partnered with a wire cutter that looks and behaves exactly Like a Xuron sprue cutter. I think I paid about $8 on sale for both tools packaged together. The final items I use are a pair of miniature smooth-jawed square jewelers pliers, and a smooth jawed needle nose plier I got in a set of miniature pliers from HD several years ago. All these tools are perfect for holding small flat parts while filing or sanding off metal “nubs”.
Here’s the Electronics set from HD, although they’ve gone up a bit in price:https://www.homedepot.com/p/Crescent-4-in-Shear-Cutter-Plier-Set-2-Piece-S2KS5NN/310771484
If you go to the Micro-Mark on line catalog, and type in “Smooth Jaw” a bunch of pliers and tools suitable for gripping PE will come up.