just an idea: Assuming you're working in a windows network environment and active directory is enabled. Try creating a security policy that disables icons from appearing on the taskbar on client machines. This would hide the R and enable you to continue using RADMIN.
If you're not in any kind of network, you could go into the taskbar properties and "always hide" RADMIN. This is also assuming the end user doesnt know how to do this.
Im on windows 2000 pro, and it does not have a taskbar option to hide that particular icon. On XP it does, but not on 2000. I also tried to create a security policy, but create new is not an option. Any other ideas?