I guess that depends on whose opinion you accept regarding what is or is not canonical.
Perhaps Superman can simply burn it off by flying into the Earth's yellow sun. Perhaps all Kryptonian condiments were destroyed when the planet exploded, rendering the question moot. Perhaps the whole idea of Krptonian mustard is just silly.
When we ask questions about stories, the answers are dependent only upon whom we accept as a legitimate author, and which authors' work we reject as non-canon. Anyone can author fan-fic, and debates about the validity of any particular part of the complete body of work are futile.
Why would God make it hard or impossible for souls in heaven to help? Is God mean and spiteful? Does this seem to hold up the concept of God as good and all powerful, or is it yet another example of a Universe that operates without a God?
Canonically, the Bible speaks of a heaven. The nature of heaven unstated as such. My little question is meant to ask some questions that make the idea of heaven seem even more remote and unlikely.
Do you think this might make a few Christians think harder about the nature of God, heaven and the goodness of God?