[Samba] useradd with "$" character within loginname

[dr.no]

any help welcome
thanks

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how can i tell the useradd(8) command to add an user which contains a "$" character within it's loginname?
it only allows alphanumeric characters for a loginname! i need this "$" character 
for the automatic creation of a machine-account for my samba server (PDC). 

(smb.conf parameter: add user script = adduser -d /dev/null -s /sbin/nologin MACHINENAME$ )
quoting or escaping "$" does not work. (e.g. adduser NAME\$)    
adduser under linux does not complain about a $, how to solve this problem under openbsd?