If I understand correctly, you need Reader 11 for one user. My suggestion would be to install Reader locally on that person's machine.
There are a few issues with what you're trying to do:
- Acrobat 9 has been end of lifed and is a rather old product in software years.
- Because 9 is EOL, installing with Reader 11 is unsupported, and no one at Adobe would know if it works.
- Acrobat 9 is not supported on your version of WTS. See Windows Terminal Services — Enterprise Administration Guide
- Setting the default handler via registry manipulation is unsupported and unlikely to be possible. It requires (for earlier product versions at least), running/invoking the installer. Use the Wizard or run from the cmd line with certain properties set: See Adobe Properties — Enterprise Administration Guide.
Still, you can experiment and might be able to make it work, but it might be worthwhile considering the time cost vs the eventual benefit.
hth,
Ben