... not as a bareword, but as a literal string, ...

Provided the bareword is a “single identifier” (i.e., something that would be a valid variable name if preceded by the appropriate sigil), Perl parses it as a string literal when it’s used as a hash subscript. From the Camel Book (4^th Edition, p. 70):

As in some shells, you can put braces around the identifier to distinguish it from following alphanumerics: "How ${verb}able!". An identifier within such braces is forced to be a string, as is any single identifier within a hash subscript. For example:

$days{"Feb"}
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can be written as:

$days{Feb}
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and the quotes will be assumed. Anything more complicated in the subscript is interpreted as an expression, and then you’d have to put in the quotes...

(Emphasis added.)