Ok, after some playing around, I thought I would share the answer for others that may need it.
You can still modify the /etc/aliases file with all the aliases you need. As a note, you will need to specify the domain/virtual domain or it will go to the local mail spool in /var/spool/mail for the user.
It would be nice to have this option in the Zentyal interface, but I could not find it.
Also, after you make the change, you must run the newaliases command to record the information.
Here is an example of the file for reference:
cat aliases
# See man 5 aliases for format
clamav: root
root: useraccount@domain.com <--- this is what I added
#Added by eBox. Postmaster alias will be rewritten in each Zentyal mail system restart but other aliases will be kept
postmaster: root
Hope this helps!
Joe