man smb.conf tells me of the parameter:
guest account (G)
This is a username which will be used for access to services which are specified as guest ok (see below). Whatever privileges this user has will be
available to any client connecting to the guest service. This user must exist in the password file, but does not require a valid login. The user
account "ftp" is often a good choice for this parameter.
On some systems the default guest account "nobody" may not be able to print. Use another account in this case. You should test this by trying to log
in as your guest user (perhaps by using the su - command) and trying to print using the system print command such as lpr(1) or
This parameter does not accept % macros, because many parts of the system require this value to be constant for correct operation.
Default: guest account = nobody # default can be changed at compile-time
I suspect that if you set/change this, in the
[global] section of your smb.conf, it will do what you want.