More VMS

As an aside to the current VMS discussion, does anyone know of an equivalent to the Unix "su -" command for VMS? Basically I'd like to be able to use my "normal" AL account for messing about with but occasionally "su" to SYSTEM to get at a protected file or directory. All the FAQs and manual pages I've come across so far point to SPAWNing a new process and then changing the privileges (eg SET PROC/PRIV=SYSPRV), which defeats the object of the exercise since the "AL" account needs system privileges in order to do the SET PROC/PRIV in the first place :-) At the moment I'm using an ST running UNITERM hooked up to a 3100/30's console port so I'm stuck with just the one login session at a time - occasionally I'd like to be able to flip over to SYSTEM without having to mess about with logging out of AL and into SYSTEM and back :-) Any ideas? Cheers Al.