General :: Recalculate Variable For Each Pass Of An Until Loop?

I am trying to write a script that will find any user on the server running more than one instance of the epiphany web browser process, then kill all their epiphany pids. (This is necessary sometimes to cure lockups, and repeat processes are the telltale sign in this case). I have tried implementing the until loop:

Code:
USER=`ps aux | grep epiphany | grep -v grep | sort | uniq -d -w 5 | awk '{print $1}'`
until [[ "$USER" == "" ]]
do
ps aux | grep epiphany | grep -v grep | grep $USER | awk '{print $2}' | sudo xargs kill
done

Unfortunately, the script only calculates the USER variable once at the beginning of the script. Fair enough, that's how it's written. My question is, how would I get the USER variable to update for each pass of the until loop so that it could cure multiple users of this ailment if necessary? That is, calculate $USER, kill their epiphany pids, repeat those two steps until the $USER variable comes up blank, then exit.