You can also use the explicit CREATE LOCAL TEMPORARY TABLE described in the ddl section. I believe this is a regression from https://issues.jboss.org/browse/TEIID-1177. As long as you are using Teiid 7.1 or later you should be able to just issue:
insert into #temptable123 select sysid,name from demodata.user
and it will infer the appropirate column names. I've logged https://issues.jboss.org/browse/TEIID-1872 to address this.
Thanks Hawkins. That works.