I suspect this is an XY Problem, but you can do this using Symbolic references. This will not work with strict refs in place (you do use strict, right?), so your code might look like

my $x = 'Foo';

my $sub_ref = do {
    no strict 'refs';
    \&{$x};
};
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so your code might look like

my $x = 'Foo';

my $sub_ref = \&{$x};
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Update: It appears my $sub_ref = \&{'Foo'}; passes strict when &{'Foo'}; does not. Huh?