For a spiked wig, one way to make spikes is not to gel the entire spike, but just hair-cement the tip of the spike together, which will make the rest of the hair hold the spike shape. My friend Hashi did this for
her Sora wig and it looked fine. It will probably be a little more difficult in a ponytail, but when you take out the hair tie, the spikes should still look okay I think. Of course, anytime you take out a pony tail, it'll look a little funky cuz real life isn't as pretty as anime. : P But if you shake it out of the pony tail, it should look okay, even if you lose a few spikes. You'll have to experiment obviously, but I think it may work better if you spike the hair outside of the ponytail, then put the ponytail in and adjust it some. It may not work at all, but it's worth a try. ^^; Hope some of that helps!