I guess I'm not that much of a foot tickler. Maybe that's a rarity in this group. Maybe this makes me even more of a rarity, but we never use devices or paraphernalia to immobilize her person, although I do enjoy using gadgetry as tickling devices. Regarding the former, I've asked many times for her to let me tie her or put things on her person. She has always demurred saying I have no problem holding in any position I like, so there will be no immobilizing devices, end of discussion.
When I do tickle her feet, what I usually do is put her on the floor on her back and pull her feet up over the arm of an easy chair of, the end of a bed, or, more often, the arm of a sofa. Then I hook one leg over her ankles. Usually her lower back and hips are up from the floor a bit so her own weight and gravity supply the pressure to hold her in place. In this position, it's fun to watch her roll and thrash about. She also tries to pull herself up on the arm of the sofa (or whatever). What's fun about this is since she started having babies a long while ago, her stomach muscles really don't cooperate, but it is a real tease to make her try.
Usually, my device of choice is a comb and my fingers. As for the curling of her toes, I love that when I'm tickling her soles. It's such a delight because feet aren't designed to protect themselves from a tickler. Usually on the soles, I tickle with my fingers.
However, I agree that the toes need to be stretched out for the best in toe tickling. Here I usually tell her and show her what I'm going to do to her which I think makes the teasing a little more fun. A couple months ago I had her in this position. I had tickled her soles for a time. Then I stopped to give her a breather. These days I use one of her combs for this. It's a pink comb that has teeth for about half its length, and a handle that comes to a rounded point at the end. I took the comb and sshowed it to her, and sort of twirled it around like you would a feather. She had already been laughing and begging for mercy, and rolling back and forth and pounding her fists on the floor.
When I twirled the comb she started screaming. So I just grabbed her by one big toe with ond hand and pushed it backward. I think just grabbing her toe probably tickles some, and the anticipation has to be torture. I used the comb as a saw on the base of her toes which always gets the best reaction. She tries SO hard to reach up and get a hand on the edge of the sofa arm. Her stomach muscles make this nearly impossible, but I encouraged her to keep trying by continuing to saw at those toes.
I also used the comb to get down between her toes, and she has four such places on both feet. I love tickling them all one by one.
After this kind of tickling, her hair is a always mess. Whatever she is wearing is always twisted and sideways. She tries as hard as she can to me mad at me. Yet she usually just attacks to try to teach me a lesson I won't soon forget, but ends up sitting on my lap. Whatever she starts then I give her exactly two hours to stop.
Anyway, in our tickling, my hand is the only thing I am allowed to use to stretch out her toes, but it works.
Hiram