Another version is a 2-petal shot-cup formed from a long rectangle of heavy paper or light card stock, with a width of half your bore circumference (or a bit wider for a little overlap) and a length of twice the height of your shot charge plus the width of your bore. Set the end of your wad-starting dowel in the middle of the paper, fold the two petals up along the dowel and wrap them around it, tuck under the two corners you get on the bottom where the edges of the petals meet (or overlap a bit), and slide it in on top of your cushion wad or a card. Things go a bit easier if you form these up ahead of time and set the creases and such, then open them out flat for carrying. Then if your material is stiff enough and your bore is large enough or your fingers skinny enough, you may even be able to just use your finger for forming and loading in the field.
Regards,
Joel