You can use Microsoft's devcon utility to disable a driver from the command-line. devcon is like a command-line Device Manager; you can list devices, enable them, disable them, etc. See this answer for some basic examples.
With devcon and administrator privileges, you can create a script that disables the sound driver. Then set it as a login script for that user via the Group Policy editor.
You'd also need to create a re-enabling script -- either set as a logoff script for that user, or as a login script for everyone else. If you don't, your users will have to reenable the soundcard manually.
See this answer (thanks, Ivo) for how to assign a login script to a user or group, as well as a handy scripting howto.
Note: This may not be enough; just because devcon disables a device doesn't mean the problem user can't just re-enable it from the Device Manager. You'd have to restrict the account through other means to prevent that.