How do I attach per vertex data in my obj file?

It looks like the obj file specification allows vp lines with arbitrary data associated (1 2 or 3 floats). I don't see how I can do that through Model IO.
The circumstance is that I have some old models created by an artist and he attached values required to animate onto the vertices. I have a proprietary format for the data and it is stored in resource forks. I'm trying to export the data into obj files to modernize. I tried to set up a submesh with the data as the vertices but Model IO eats them if I don't include faces into the submesh. I don't need faces.
I can hook or crook this problem by adding faces, but I'd like to do it the way that the API intends for such things to be done.
Thanks,

Jim