mknod will work, with some exceptions. The syntax is:
mknod /path/to/new/dev c major minor
So, for example, you should likely be able to create a new pts type device with
mknod /tmp/mypts c 136 0
What I've found, however, is that if you try to do this in /dev/pts, you will get an access denied message. I can do it in /dev, just not /dev/pts. I'm on a Centos 5.5 box. YMMV.
This is because /dev/pts is mounted by the kernel (from my /etc/fstab file):
devpts /dev/pts devpts gid=5,mode=620 0 0
This is a kernel-managed pseudo filesystem, and I wouldn't think that screwing around with it is a good idea. The standard way to get a new file created in there is by open()ing /dev/ptmx; that will get the calling process the fd of the master terminal assigned, and a new device will be created as /dev/pts/X where X is dynamically allocated by ptmx as the slave. This would then be opened itself, usually by a forked process from the original one.
There's likely a good reason why it's done this way. I'm not sure what it is, but I would avoid trying to break it, if system stability is something you value.
That all being said, the first command line with real options I presented would allow you to make your own pts device anywhere but /dev/pts, and depending on what you're intending to do with it, maybe that's enough to get you where you're going.