Success! I have got it working with an editor, although not exactly a lightweight one.
I have used remote X and X over ssh but on my LAN, but it will probably be sluggish to a server on the other side of the world. In any case I need to connect to multiple shared hosting web servers which do not have X installed.
I am pretty sure that PCMan does not issue a command for the remote server to open a terminal,it opens a terminal locally, possibly passing the path as an argument.
I think I have found why vim does not work. PCMan passes a url like this:
Which looks right to me, but vim wants:
I am going to try writing a wrapper script that sends what vim wants.
In the meantime this does mean it will work with Komodo Edit if supplied the right command line. I do need to re-enter my password, and Komodo is hardly light. On the other hand Komodo looks like a good editor (I am trying it out, and I will suggest the open source version in package suggest if it lives up to expectations).