Try this:
set interface ge-x/y/z ether-options ethernet-switch-profile tag-protocol-id
Does this help? ELS Translator does not translate this properly, if indeed the syntax above is correct. BTW, I found this info in attached new Day 1 Book covering ELS EX operation.
Now Q-in-Q config on ELS platforms is MUCH different than with legacy platforms. For detailed info look here. You should for sure be able to mix dual-tagged and single tagged VLANs on the same Q-in-Q enabled Interface.
Good luck.