cvsup between levels, single user issue

[Chris]

I was going to attempt an in-place upgrade of a light load server  
running 5.3 to bring it to 6.1 RELEASE P6 (RELENG_6_1). I read in  
UPDATING that going between 5.x and 6.x requires single user mode  
which isn't an option on a remote machine (though I can stop  
sendmail, bind, popper etc manually but not that which keeps me on  
like sshd). I've not taken a machine to single user yet during my  
builds but have always had the box in my possession and on my private  
net when I've done that. I saw threads even today that left the issue  
somewhat up in the air. I still need to protect the machine. Would a  
doable jump be to move the machine to RELENG_5_5 remotely or would  
that most likely be unsuccessful without going single user? There is  
no exotic hardware on the box.