'  Update the attribute for the current user
   IUserObject.PutEx ADS_PROP_UPDATE, Attribute1, (usArray)
%>

One could use the Put method here instead of PutEx.  Most ADSI implementations allow setting multi-value attributes with Put.  However, more functionality is exposed for the PutEx method such as erasing as well as appending data to the user's attribute.  It simply requires one extra argument.