I am afraid it will not work. Each process has own copy of environ variables and BAT file (or external program) will be able to change that copy. It will not be able to change environ variables those available to HostMonitor.
In version 4 will be implemented list of users, each will have set of rights (e.g. manage report profiles, manage action profiles, etc) and some properties like e-mail address, ICQ address, pager number. You will be able to specify these properties in the actions using macro variables.