Xhost might be able to help you.
xhost +<username> or xhost +, depending on how you want to do it.
From the xhost man pages:
[+]name The given name (the plus sign is optional) is added to the list allowed to
connect to the X server. The name can be a host name or a user name.
+ Access is granted to everyone, even if they aren't on the list (i.e., access
control is turned off).
See the man pages and google searches for more information.