Ok, before you begin to go down this route a word of warning.

By default Citrix has "per user associations" switched off. If you want an individual login to have different associations you must switch "per user associations" on.

Read up on this before you do it, as it will cause more problems than it fixes. The most significant problem (under MF 1.8 at least) is that it bloats the registry by an enormous amount. As the registry has a finite maximum you can quickly reach this size and end up in a lot of trouble.